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Year 7 ScienceActivity packPhysics
• Your work for this topic is separated into lessons.
• You should aim to complete one lesson in every Science slot
on your timetable.
• Don’t worry if you can’t complete all the tasks. Choose things
that are at a level you feel confident at.
• If you need some help and support, use the information in blue
on the pages. If you have access to the internet, then use BBC
Bitesize KS3 “Forces” “Pressure” and “Density” topic areas to
find any extra information – although you may not need it!
Forces
Forces
Task Description
1 Speed
How to find the speed of an object
Explain what speed is
2Distance-time graphs
Describe features of distance-time graphs
Draw distant-time graphs and describe the motion of the object
3Relative motion
What is relative motion and calculate it for simple situations
Apply the idea of relative motion to overtaking and collisions
4Forces
Identify forces acting on an object
Calculate the resultant force on an object
5Gravity
Describe what gravity is
Describe what is meant by weightless
6
Mass, weight and gravity
How does mass affect weight
Use the equation linking mass and gravity to find weight
Explain what causes an object to have weight and why it can change
Glossary
Key term Definition
Speed
Average speed
Relative motion
Acceleration
Weight
Non-contact force
Contact force
Mass
Gravitational field strength
Field
Fill this in as you work through the booklet
Lesson 1Speed
Learning Objectives:List the factors involved in defining speed.Describe a simple method to measure speed.Use the speed formula
Distance and Speed
When you travel on a journey, it takes a certain amount of time to travel the distance. The speed of a vehicle is worked out from how far a journey is and how long it takes. The units used for measuring speed are metres per second (m/s).
A car’s speedometer shows the car’s speed at each instant
Activity
What does speed measure?
__________________________________________________________________________________
Which two quantities are needed to work out the speed at which something is travelling?
__________________________________________________________________________________
If car A travels 2 metres in one second and car B travels 2.5 metres in two seconds, which has the
higher speed?
__________________________________________________________________________________
__________________________________________________________________________________
Write three commonly used abbreviations for speed
__________________________________________________________________________________
When travelling fast your speed is high. You cover a longer distance in a certain time – you travel more metres in each second, compared with travelling slower
Activity
Use a tape measure to measure out 10m. Time how long it takes to walk, run, hop, crawl the 10m.Record your results in the table below, make sure you round your results to the nearest second.Use your results to calculate your speed.
Speed MeasurementTwo people are travelling on a road 10km long.
10km If one person takes 1 hour to travel 10km we say they are travelling 10km per hour –this is shown as 10km/hThe other person takes 2 hours to complete 10km this means they only travel 5km in 1 hour so their speed in 5km per hour (5km/h).We can calculate an objects speed by dividing its distance by the time taken. We use the formula:
Speed = Distance travelledtime taken
Method of travel Distance travelled (m)
Time taken rounded to the nearest second (s)
Speed = Distancetime
Run
Walk
Crawl
Hop
Example calculation:Usain Bolt won the 2016 Olympic 100-metre final in a time of 9.81 seconds.Usain’s speed = 100 ÷ 9.81 = 10.19m/sThis is equivalent to about 37km/h or about 23mph.
The figures below are for the distances that someone drives on different journeys and the time ittakes. Use the speed formula to calculate the speed for each journey.
a) 100 m in 20 seconds……………………………………………………………………………………………………………………………………………………………………b) 48 m in 4 seconds……………………………………………………………………………………………………………………………………………………………………c) 57 m in 3 seconds……………………………………………………………………………………………………………………………………………………………………d) 3 km in 100 seconds……………………………………………………………………………………………………………………………………………………………………e) 1 km in 1 minute……………………………………………………………………………………………………………………………………………………………………f) 350 km in 5 hours……………………………………………………………………………………………………………………………………………………………........
Practising Speed Calculations.
When Usain Bolt won the Olympics sprint in 2016, his speed varied during the race. At the start it took a while to get up to full speed. The speed of 10.19 m/s that we calculated is his average speed over 100 metres. His top speed was over 12 m/s.Some speed cameras work out a car’s average speed over a distance of a kilometre or so, while other types work out speed almost in an instant. A car’s speedometer displays the exact speed at any moment.
Average Speed
Explain why your average speed and your top speed over a car journey will be different.
____________________________________________________________________________________
___________________________________________________________________________________
What benefit to road safety may there be when cameras work out average speed over a distance, rather
than in one spot?
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Use the following page to research and design a poster on speed cameras.
Things to include:
The difference between average speed and instant speed
Different types of speed cameras
How they work
Are they safe
Lesson 2Distance-time graphs
Learning Objectives:Gather relevant data to describe a journey.Display the data on a distance–time graph
Activity
Set up a small ramp using a book leaning against the sofa on the floor. Get a ball and roll it down the
ramp letting it come to a complete stop
.
Describe the journey of the ball – think about its speeds at different points.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
We can use a distance-time graph to represent journeys. A family of cyclists are travelling at a steady speed along a path. This means that they cover the same distance every second.For every second that passes, the cyclists travel 5m. After 10s they are 50 m from the starting point.This can be shown on a graph like the example below:
The Y-axis shows us how far the object has travelled from its starting point. The X-axis show us how much time it took to reach it distance.
What unit should be used to measure the cyclists’ speed in the previous example?
___________________________________________________________________________________
Use the graph to work out how far the cyclist travels in the first 6 seconds of their journey?
___________________________________________________________________________________
What was the cyclists’ speed across the journey?
___________________________________________________________________________________
Describe or sketch a line graph to show another cyclist who is travelling at half the speed. How does it
differ from the previous graph?
Dis
tan
ce (
met
ers)
40
20
30
10
50
Tme (seconds)2 4 6 8 10
Distance-time graphs can show us when an object is travelling fast or slow, accelerating (getting faster), or decelerating (getting slower)
Changing Speed
In this journey the cyclist does not travel the same distance every second. For the first 10 s they travel at a slow speed and cover little distance. However, they gradually accelerate (speed up). If an object is stationary for part of its journey it is represented by a flat line on the graph. This is because no distance is being travelled but time is passing. If an object is getting faster it is shown with a curved line. This is because it is covering more distance in less time as it speeds up.
Use the graph to describe the different parts of a journey. This journey will last 60 minutes.
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
Use the following data to draw a distance-time graph using the graph paper on the following page. The table shows a journey made by someone pushing a trolley in a supermarket aisle.
Drawing a distance-time graph
Time (s) 0 5 10 15 20 25
Distance travelled (m)
0 1.5 3.0 4.5 6.0 7.5
Once you have drawn the graph answer the following question:
Which of the following statements best describes the journey?i) The person gets faster as time goes on. ii) The person stops at 5 s intervals.iii) The person travels at a constant speed. iv) The person takes 15 s to travel 0.5 m.
Lesson 3Relative motion
Learning Objectives:Describe the motion of objects in relation to each other.Explain the concept of relative motion.Apply the concept of relative motion to various situations.
When scientists compare the movement of two objects, they talk about relative motion.For example, if a car is travelling at 50 km/h and is being caught by a car doing 55 km/h, the speed of the second car relative to the first – its relative speed – is 5 km/h.
If a cyclist is doing 20km/h and a car is doing 60km/h.
What is the speed of the car relative to the cyclist?
_____________________________________________________________________________________
Remember the speed equation for the next question:
Speed = distance travelled
time
A person sets off jogging along a canal path at 12 km/h at the same time as a boat sets off at 10 km/h.
a) How far will each one travel in half an hour?
_____________________________________________________________________________________
_____________________________________________________________________________________
b) What is their relative speed?
_____________________________________________________________________________________
Relative Motion
We can put this in a formula triangle to help us rearrange the equation to find the other variables.
XS
d
t
DistanceMeasured in metersdistance = speed X time
TimeMeasured in secondsspeed = distance + time
SpeedMeasured in m/sSpeed = distance + time
Journeys and Collisions
Two cars travelling at 40 km/h towards each other have a relative speed of 80 km/h. This is equivalent to a moving car approaching a stationary car at 80 km/h
Using this idea explain why head-on collisions of two moving vehicles are so dangerous?
____________________________________________________________________________________
____________________________________________________________________________________
___________________________________________________________________________________
Explain the similarities and differences between these situations:
a) a car travelling at 10 km/h and colliding with a parked car;
b) a car travelling at 70 km/h and colliding with a car doing 60 km/h in the same direction;
c) a car travelling at 70 km/h and colliding with a car doing 60 km/h in the opposite direction.
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
Lesson 4Forces
Learning Objectives:Recognise different examples of forces.List the main types of force.Represent forces using arrows.
Using the images to help list as many forces as you can:
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
A force can be a pushing force, a pulling force or a turning force. There is a pulling force from the Earth on people and objects. This pulling force is known as gravity
Types of Forces
__________________ – pulls things
downwards.
______________
________________________________
_ (drag) – acts against anything
moving through air
__________________________ – acts
against anything moving
________________________________
– keeps things afloat
A force can be a pushing force, a pulling force or a turning force. There is a pulling force from the Earth on people and objects. This pulling force is known as gravity
Complete the sentences below with the correct force
Types of Forces
Words : upthrust, air resistance, friction, weight
When labelling forces on a diagram we use an arrow to show:The direction the force is acting How big the force is
Label the car using arrows with all the forces acting on it. Make sure your arrows touch the object, use a ruler and a pencil
A number of forces can be acting on something at the same time. Look at the picture of an aeroplane below, multiple forces are acting on it:the downward pull of gravity;the forward push from the engines;the upward pull provided by the lift from the wings;the pushing force of the air which resists the plane as it moves.The direction of a force can be shown by an arrow. We can show how strong one force is compared to another by using different-sized arrows.
Multiple Forces and Force Diagrams
When forces are in balance there is no change in movement. This means each force is perfectly balanced by an equal force in the opposite direction. Think of it like two tug of war teams pulling equally in opposite directions so no one is moving.
Forces in Balance
Resultant Force
When two forces acting on an object are not equal in size, we say that they are unbalanced forces. The overall force acting on the object is called the resultant force. If the forces are balanced, the resultant force is zero
What would happen to the size and direction of the resultant force if an extra person were added to the
left-hand team?
____________________________________________________________________________________
____________________________________________________________________________________
.
Sketch a car that is starting to move away from a set of traffic lights. Draw arrows to show the forces at
work and comment on the direction of the resultant force.
Draw force diagrams and calculate the size and direction of the resultant force if:
a boat has a force of 500 N from the wind pushing it forwards and the water resistance is 200 N
a sledge is being pulled with a force of 250 N and acted on by friction (100 N) and air resistance (50 N).
Lesson 5Gravity
Learning Objectives:Describe gravity as a non-contact force.Explore the concepts of gravitational field and weight.Explain how weight is related to mass
The area around the Earth affected by its gravity is its gravitational field. A field is an area in which an object feels a force.
Earth’s Gravitational Field
Within the Earth’s gravitational field objects are pulled towards the Earth. This pull is a non-contact force because it acts at a distance – objects do not have to be on a planet’s surface to be affected.
Contact and non-contact forcesNon-contact forces such as gravity do not have to be touching an object to have an effect on it.Contact forces must be touching the object in order for it to feel the force.
List some contact forces we have learnt about so far:
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Describe what is meant by a gravitational field.
_____________________________________________________________________________________
_____________________________________________________________________________________
Gravitational field strength (g) is measured in newtons per kilogram (N/kg). The Earth's gravitational field strength at, or close to, the surface is 10 N/kg. This means that for each kilogram of mass, an object will experience 10 N of force. This gets weaker the further you are away from the Earth.
The weight of an object is a force. It is the force acting on the object due to gravity. It depends on the mass of the object and the strength of the gravitational field acting on it.
Where there is a weaker gravitational field, the weight of an object is smaller. For example, the gravitational field strength of the Moon is 1.6 N/kg.Therefore, an astronaut will weigh less on the Moon than they do on the Earth
We measure weight in newtons (N), mass is measured in grams or kilograms. This is what we use a mass balance to find.
The formula used to calculate weight is
Weight of an object (N) = mass of the object (kg) X gravitational field strength (N/kg)
ExampleOn the surface of the Earth the gravitational field strength is about 10 N/kg. To calculate how much a bag of fruit with a mass of 2 kg would weigh on the Earth’s surface:
Weight = mass X gravity2kg X 10N/kg = 20N
Find the mass of some objects around your home. You can do this either using scales or you can use objects that have their mass stated on a packet.
Remember the unit for mass is grams or kilograms.If you find a mass in grams you must convert this to kilograms
Grams Kilograms X 1000
Object Gravitational field strength of Earth (N/kg)
Mass (kg) Weight (N)
Lesson 6Mass, Weight and Gravity
Learning Objectives:Explain the difference between mass and weight.Understand how gravity varies according to where you are in the solar system.Apply ideas about gravity to various situations.
WeightThe weight of an object is the force of gravity pulling down on the object. If there were no gravity then everything would be weightless.
Because weight is a force, it should be measured in newtons. We can measure the weight of an object using instruments such as newton-meters. This measures how much the object is pulled down by gravity.
MassMass is a measure of the amount of material in an object – the number of particles and type of particles it is composed of. Mass does not depend on the force of gravity, so it does not change if you take it somewhere where the gravitational field is not as strong, such as the Moon.
Mass is measured in kilograms. The mass of an object can be measured using a balance.
Understanding Mass and Weight
Complete the table to find your weight on all the planets in the solar system.Use the equation you learnt last lesson:
Weight = mass X gravity
Place Pull of Gravity (N/kg) My Mass (kg) My Weight (N)
Earth 10
Moon 1.7
Outer Space 0
Jupiter 26
Mercury 4
Venus 8
Neptune 12
1. Why does your mass stay the same?
____________________________________________________________________________________
____________________________________________________________________________________
2. Why does your weight change?
____________________________________________________________________________________
____________________________________________________________________________________
3. Where is your weight largest? Why?
____________________________________________________________________________________
____________________________________________________________________________________
5. Name another planet where your weight would be
(a) Lower than Earth
____________________________________________________________________________________
(b) Greater than Earth?
____________________________________________________________________________________
Gravity in SpaceThe force of gravity on you (your weight) depends on your distance from a planet. The further away you are from the Earth, the weaker the gravitational field strength, so the weaker the force pulling you back. In outer space, the distance to the nearest planets and stars could be so big that there would be no noticeable force of gravity – you would be weightless.
Why, when travelling from the Earth to the Moon, would the weight of the astronauts become less the
further they got from the Earth?
____________________________________________________________________________________
___________________________________________________________________________________
How did their weight change when they got nearer to the Moon?
____________________________________________________________________________________
____________________________________________________________________________________
Why do you think they weighed less on the Moon?
____________________________________________________________________________________
____________________________________________________________________________________
ForcesAnswers
Lesson 1Speed
Learning Objectives:List the factors involved in defining speed.Describe a simple method to measure speed.Use the speed formula
Distance and Speed
When you travel on a journey, it takes a certain amount of time to travel the distance. The speed of a vehicle is worked out from how far a journey is and how long it takes. The units used for measuring speed are metres per second (m/s).
A car’s speedometer shows the car’s speed at each instant
Activity
What does speed measure?
The distance an object travels in a certain amount of time
Which two quantities are needed to work out the speed at which something is travelling?
Distance and time
If car A travels 2 metres in one second and car B travels 2 metres in two seconds, which has the
higher speed?
Car A
Write three commonly used abbreviations for speed
m/s
Km/h
mph
When travelling fast your speed is high. You cover a longer distance in a certain time – you travel more metres in each second, compared with travelling slower
Activity
Use a tape measure to measure out 10m. Time how long it takes to walk, run, hop, crawl the 10m.Record your results in the table below, make sure you round your results to the nearest second.Use your results to calculate your speed.
Speed MeasurementTwo people are travelling on a road 10km long.
10km If one person takes 1 hour to travel 10km we say they are travelling 10km per hour –this is shown as 10km/hThe other person takes 2 hours to complete 10km this means they only travel 5km in 1 hour so their speed in 5km per hour (5km/h).We can calculate an objects speed by dividing its distance by the time taken. We use the formula:
Speed = Distance travelledtime taken
Method of travel Distance travelled (m)
Time taken rounded to the nearest second (s)
Speed = Distancetime
Run 10 3 3.3
Walk 10 6 1.7
Crawl 10 5 2
Hop 10 8 1.25
Example calculation:Usain Bolt won the 2016 Olympic 100-metre final in a time of 9.81 seconds.Usain’s speed = 100 ÷ 9.81 = 10.19m/sThis is equivalent to about 37km/h or about 23mph.
The figures below are for the distances that someone drives on different journeys and the time ittakes. Use the speed formula to calculate the speed for each journey.
a) 100 m in 20 seconds100 / 20 = 5m/s
b) 48 m in 4 seconds48 / 4 = 12m/s
c) 57 m in 3 seconds19m/s
d) 3 km in 100 seconds3km = 3000m3000 / 100 = 300m/s
e) 1 km in 1 minute1km = 1000m 1min = 60seconds
1000 / 60 = 16.7f) 350 km in 5 hours……………………………………………………………………………………………………………………………………………………………........
Practising Speed Calculations.
When Usain Bolt won the Olympics sprint in 2016, his speed varied during the race. At the start it took a while to get up to full speed. The speed of 10.19 m/s that we calculated is his average speed over 100 metres. His top speed was over 12 m/s.Some speed cameras work out a car’s average speed over a distance of a kilometre or so, while other types work out speed almost in an instant. A car’s speedometer displays the exact speed at any moment.
Average Speed
Explain why your average speed and your top speed over a car journey will be different.
Calculation of average speed uses the whole distance and the total time for the journey. During a
journey you need to slow down and speed up at appropriate times.
What benefit to road safety may there be when cameras work out average speed over a distance, rather
than in one spot?
Drivers could slow down briefly for a camera measuring at one spot but exceed the speed limit the rest
of the time. Cameras that work out the average speed over a long stretch of road will be able to tell if
drivers do this.
Use the following page to research and design a poster on speed cameras.
Things to include:
The difference between average speed and instant speed
Different types of speed cameras
How they work
Are they safe
Lesson 2Distance-time graphs
Learning Objectives:Gather relevant data to describe a journey.Display the data on a distance–time graph
Activity
Set up a small ramp using a book leaning against the sofa on the floor. Get a ball and roll it down the
ramp letting it come to a complete stop
Describe the journey of the ball – think about its speeds at different points.
When the ball sets off down the ramp it gets faster.
When it reaches the floor it begins to slow down.
The ball eventually stops.
We can use a distance-time graph to represent journeys. A family of cyclists are travelling at a steady speed along a path. This means that they cover the same distance every second.For every second that passes, the cyclists travel 5m. After 10s they are 50 m from the starting point.This can be shown on a graph like the example below:
The Y-axis shows us how far the object has travelled from its starting point. The X-axis show us how much time it took to reach it distance.
What unit should be used to measure the cyclists’ speed in the previous example?
m/s
Use the graph to work out how far the cyclist travels in the first 6 seconds of their journey?
30m
What was the cyclists’ speed across the journey?
Distance travelled = 50m time taken = 10s
50 / 10 = 5m/s
Describe or sketch a line graph to show another cyclist who is travelling at half the speed. How does it
differ from the previous graph?
Dis
tan
ce (
met
ers)
40
20
30
10
50
Tme (seconds)2 4 6 8 10
25
Use the graph to describe the different parts of a journey. This journey will last 60 minutes.
For ten minutes I drove to the train station. I waited ten minutes for a train. I got on the train which
travelled at a fast pace for 7.5 minutes. We arrived and waited at the platform for 2.5 minutes before
alighting. I walked around the park for 25 minutes before resting on a bench.
Use the following data to draw a distance-time graph using the graph paper on the following page. The table shows a journey made by someone pushing a trolley in a supermarket aisle.
Drawing a distance-time graph
Time (s) 0 5 10 15 20 25
Distance travelled (m)
0 1.5 3.0 4.5 6.0 7.5
Once you have drawn the graph answer the following question:
Which of the following statements best describes the journey?i) The person gets faster as time goes on. ii) The person stops at 5 s intervals.iii) The person travels at a constant speed. iv) The person takes 15 s to travel 0.5 m.
Dis
tan
ce (
met
ers)
4.5
1.5
3
0
6
Tme (seconds)
5 10 15 20 25
7.5
Lesson 3Relative motion
Learning Objectives:Describe the motion of objects in relation to each other.Explain the concept of relative motion.Apply the concept of relative motion to various situations.
When scientists compare the movement of two objects, they talk about relative motion.For example, if a car is travelling at 50 km/h and is being caught by a car doing 55 km/h, the speed of the second car relative to the first – its relative speed – is 5 km/h.
If a cyclist is doing 20km/h and a car is doing 60km/h.
What is the speed of the car relative to the cyclist?
40km/h
Remember the speed equation for the next question:
Speed = distance travelled
time
A person sets off jogging along a canal path at 12 km/h at the same time as a boat sets off at 10 km/h.
a) How far will each one travel in half an hour?
Distance = speed x time 30 minutes = 0.5 of 1 hour
Jogging: 12 X 0.5 = 6km Boat: 10 X 0.5 = 5km
12km/h X 1800s =
b) What is their relative speed?
2km/h
Relative Motion
We can put this in a formula triangle to help us rearrange the equation to find the other variables.
XS
d
t
Distancedistance = speed X time
Timespeed = distance + time
SpeedSpeed = distance + time
Journeys and Collisions
Two cars travelling at 40 km/h towards each other have a relative speed of 80 km/h. This is equivalent to a moving car approaching a stationary car at 80 km/h
Using this idea explain why head-on collisions of two moving vehicles are so dangerous?
The collision speed is the combined speed of the two vehicles.
Explain the similarities and differences between these situations:
a) a car travelling at 10 km/h and colliding with a parked car;
b) a car travelling at 70 km/h and colliding with a car doing 60 km/h in the same direction;
c) a car travelling at 70 km/h and colliding with a car doing 60 km/h in the opposite direction.
Situations a) and b) have the same impact speed, 10 km/h; so the damage from the collisions will be
similar. b) Could be much worse if the driver lost control and hit a stationary object. c) The impact speed
is much higher; 130 km/h; so the consequences would be very serious.
Lesson 4Forces
Learning Objectives:Recognise different examples of forces.List the main types of force.Represent forces using arrows.
Using the images to help list as many forces as you can:
Pull, magnetism, air resistance, push, upthrust
A force can be a pushing force, a pulling force or a turning force. There is a pulling force from the Earth on people and objects. This pulling force is known as gravity
Types of Forces
gravity – pulls things downwards.
Air resistance (drag) – acts against
anything moving through air
Friction– acts against anything moving
________________________________
upthrust – keeps things afloat
A force can be a pushing force, a pulling force or a turning force. There is a pulling force from the Earth on people and objects. This pulling force is known as gravity
Complete the sentences below with the correct force
Types of Forces
Words : upthrust, air resistance, friction, weight
When labelling forces on a diagram we use an arrow to show:The direction the force is acting How big the force is
Label the car using arrows with all the forces acting on it. Make sure your arrows touch the object, use a ruler and a pencil
A number of forces can be acting on something at the same time. Look at the picture of an aeroplane below, multiple forces are acting on it:the downward pull of gravity;the forward push from the engines;the upward pull provided by the lift from the wings;the pushing force of the air which resists the plane as it moves.The direction of a force can be shown by an arrow. We can show how strong one force is compared to another by using different-sized arrows.
Multiple Forces and Force Diagrams
Air resistance
Thrust
Reaction
Friction
Weight
When forces are in balance there is no change in movement. This means each force is perfectly balanced by an equal force in the opposite direction. Think of it like two tug of war teams pulling equally in opposite directions so no one is moving.
Forces in Balance
Resultant Force
When two forces acting on an object are not equal in size, we say that they are unbalanced forces. The overall force acting on the object is called the resultant force. If the forces are balanced, the resultant force is zero
What would happen to the size and direction of the resultant force if an extra person were added to the
left-hand team?
A bigger force would be caused by the left-hand team therefore the resultant force will pull the right-
hand team towards them.
Sketch a car that is starting to move away from a set of traffic lights. Draw arrows to show the forces at
work and comment on the direction of the resultant force.
Air resistance
Thrust
Friction
Draw force diagrams and calculate the size and direction of the resultant force if:
a boat has a force of 500 N from the wind pushing it forwards and the water resistance is 200 N
a sledge is being pulled with a force of 250 N and acted on by friction (100 N) and air resistance (50 N).
Wind 500N
Water resistance200N
The resultant force pushes the boat forward with a force of 300N
Friction 100N
Pull 250N
Air resistance50N
Lesson 5Gravity
Learning Objectives:Describe gravity as a non-contact force.Explore the concepts of gravitational field and weight.Explain how weight is related to mass
The area around the Earth affected by its gravity is its gravitational field. A field is an area in which an object feels a force.
Earth’s Gravitational Field
Within the Earth’s gravitational field objects are pulled towards the Earth. This pull is a non-contact force because it acts at a distance – objects do not have to be on a planet’s surface to be affected.
Contact and non-contact forcesNon-contact forces such as gravity do not have to be touching an object to have an effect on it.Contact forces must be touching the object in order for it to feel the force.
List some contact forces we have learnt about so far:
Push, pull, air resistance, upthrust, water resistance
Describe what is meant by a gravitational field.
A gravitational field is an area in which an object feels the effect of gravity.
Lesson 6Mass, Weight and Gravity
Learning Objectives:Explain the difference between mass and weight.Understand how gravity varies according to where you are in the solar system.Apply ideas about gravity to various situations.
WeightThe weight of an object is the force of gravity pulling down on the object. If there were no gravity then everything would be weightless.
Because weight is a force, it should be measured in newtons. We can measure the weight of an object using instruments such as newton-meters. This measures how much the object is pulled down by gravity.
MassMass is a measure of the amount of material in an object – the number of particles and type of particles it is composed of. Mass does not depend on the force of gravity, so it does not change if you take it somewhere where the gravitational field is not as strong, such as the Moon.
Mass is measured in kilograms. The mass of an object can be measured using a balance.
Understanding Mass and Weight
Complete the table to find your weight on all the planets in the solar system.Use the equation you learnt last lesson:
Weight = mass X gravity
Place Pull of Gravity (N/kg) My Mass (kg) My Weight (N)
Earth 10 50 500
Moon 1.7 50 85
Outer Space 050
0
Jupiter 2650
1300
Mercury 450
200
Venus 850
400
Neptune 1250
600
1. Why does your mass stay the same?
Mass is the amount of “stuff” that makes up an object.
2. Why does your weight change?
Your weight changes as this is a force due to gravity and the gravitational field strengths change on
different planets.
3. Where is your weight largest? Why do you think?
Jupiter, it is the largest planet and has the strongest gravitational field.
5. Name another planet where your weight would be
(a) Lower than Earth
Mercury, venus, (moon)
(b) Greater than Earth?
Jupiter, neptune
Gravity in SpaceThe force of gravity on you (your weight) depends on your distance from a planet. The further away you are from the Earth, the weaker the gravitational field strength, so the weaker the force pulling you back. In outer space, the distance to the nearest planets and stars could be so big that there would be no noticeable force of gravity – you would be weightless.
Why, when travelling from the Earth to the Moon, would the weight of the astronauts become less the
further they got from the Earth?
The further the astronaughts from Earth the weaker the effects of Earths gravitational field.
How did their weight change when they got nearer to the Moon?
As they approach the moon and its gravitational field their weight will be less than on Earth but greater
than out of space.
Why do you think they weighed less on the Moon?
The gravitational field strength on the moon is lower than Earth
