Demonstrate understanding of aspects of Mechanics

Science 1.1 (AS09040)

Specific Learning Outcomes

Speed:◦Define the term speed◦Name and give symbols◦Use the relationship to solve problems◦Interpret and draw distance-time graphs◦Use the gradient to describe/calculate speed

Specific Learning Outcomes

Acceleration◦Define acceleration and it unit and symbol◦Use the relationship to solve problems◦Draw and interpret speed-time graphs◦Calculate acceleration and distance from speed-

time graphs◦Solve problems using acceleration due to gravity

where g=10ms-1

Specific Learning Outcomes

Force◦Define force as a push, pull, twist or squeeze◦Name and give symbols of units for force and mass◦Give eg of contact and non-contact forces◦Use force diagrams◦Know balanced and unbalanced forces and what

they do to an object◦Use the formula F=ma to solve problems◦Differentiate between mass and weight◦Define friction and explain how it works

Specific Learning Outcomes

Pressure◦Define the term pressure including unit and symbol◦Use the relationship to solve problems

Energy◦Explain that energy is need to make things happen

or change◦Describe different forms of energy◦Identify energy transformations◦Define gravitational potential and kinetic energy

with their units and symbols◦Use the relationships to solve problemsmvEk

21

2

Specific Learning Outcomes

Work◦Define the term work with units and symbols◦Use the relationship W=Fd to solve problems◦Use the relationships to

determine amounts of energy transferred

Power◦define the term power with unit and symbol◦Use the relationship to solve problems

mvEk21

2

SI Units in Science

Quantity Symbol SI Unit Symbol

Acceleration a Metre per second squared ms -2

Current l Ampere (amp) A

Distance d Metre m

Force F Newton N

Energy E Joule J

Mass m Kilogram kg

Power P Watt W

Pressure p Pascal Pa

Resistance R Ohm Ω

Speed s Metre per second ms -1

Time t Second s

Velocity v Metre per second ms -1

Voltage V Volt V

Work W joule J

Distance, Speed, Time

This sort of triangle can be useful for rearranging formula to find different aspects

Cover up what it is you are wanting to find and you are left with the formula eg:

Distance, Speed, Time problems

Jack wants to know how fast he can swim. What 2 measurements must he have to calculate his speed?

Write down the formula for calculating speed when time and distance are known.

Sam wants to know the distance she travelled to get to Masterton. What 2 measurements must she have to calculate this?

Write down the formula for calculating the distance when time and speed are known.

Distance, Speed, Time Problems

Hemi wanted to know the how long took for him to get to the bus. What 2 measurements must he have to calculate the time?

Write down the formula for calculating time when the distance and speed are known.

Steps in Calculations

1. Write the formula as you know it

2. Write what you know

3. Arrange the formula to show what you are looking for

4. Convert what you know to the correct units

5. Put the correct figures into the correct equation

6. Calculate the answer

7. Write the correct units  Steps 3 and 4 you only need to do if they are needed

Calculations to complete

Calculate the average speed for each of the following, make sure you write down all the steps

1. A dog runs 100m in 25s

2. A dolphin swims 720m in 60s

3. A car travels 227.5km in 3.5h

Calculations to complete

Complete these questions:1. Isla’s scooter travels at an average of 50kmh-1.

Calculate how long it will take her to travel 17 km if she does not stop.

2. Anau is cycling at an average of 12ms-1. Calculate the distance he travels in 2 minutes

3. Sally completes a biathlon in which she has to swim across a lake then cycle around it

◦Calculate Sally’s speed in Kmh-1 for the swim◦Calculate Sally’s average speed for the entire race

Section Distance TimeSwim 600m 15 minsCycle 20km 45 mins

Distance-time graphs 1

Distance-time graphs 2

Distance-time graph problems 1

1. a)

b) After 1s, what distance from the start was the object represented by line A

Calculate the speed of this objectc) From the graph, state the total number of sec the

moving object in line B was:Moving:_______Stationary: _________

Distance-time graph problems 2

Students carrying a stopwatch stood every 20m along a 100m track. They started their timer when a cyclist started moving, then stopped it when the cyclist passed their position. Here are the results:

1. Draw a distance time graph of these results2. Describe the motion during the first 60m3. Describe the motion between 60m and 100m

Distance (d) 0 20 40 60 80 100Time (s) 0 9 15 18 19 20

Distance-time graph problems 3

The distance-time graph for a dog chasing a stick is below:

Use the graph to answer the following questions:1. Calculate the dog’s speed for the first 12s2. What was the dog’s speed during the time 12-18s3. Describe the motion of the dog from the time 18-36s

Ticker timers and speed

A ticker timer can be used to record the distance and time information for a moving object. This can then be used to calculate speedEg on the next slide is a ticker timer tape

collected when a trolley with the tape was rolled along the bench.

We know that every 10 dots is 0.2 s and we can measure the distance between each of these and use this to calculate the speed

Ticker timers and speed 2

Dots Time (s) Distanc

e travelled (cm)

Total distance from start (cm)

Average speed for each section (cms-1)

Total Average speed (cms-1)

Start A 0 0 0B 0.2 1.5 1.5C 0.4 3.1 4.6D 0.6 6.4 11.0

0

1.5/0.2=7.53.1/0.2=15.56.4/0.232

1.5/0.2=7.54.5/0.4= 11.511.0/0.6= 18.3

0

Acceleration

As with the speed formula, the acceleration formula of:

can also be put into a triangle to rearrange it and solve different problems

Acceleration problems

Complete the table by calculating the different values:

Acceleration a (ms-2)

Change in speed ∆v(ms-1)

Change in time ∆t(s)

A 180 80B 2.6 0.7450 C 33.5 D 1870 300 E0.3 2.5 F

2.253.7

135063

4.38.3

Speed-time graphs

Speed-time graphs 2

Look at this graph of a bus journey:

What was the speed of the bus at 3.5s? How long did it take the bus to reach a constant speed? Work out the acceleration of the bus in ms-2 over the first 3s. What is happening to the bus over the last 2.5s of its journey? Use the graph to work out the total distance travelled during

the journey

Force, Mass and Acceleration

Forces are pushes or pulls and change the shape, speed and direction of an object

They can be contact or non-contactForces have a size and directionThe net force of an object is calculated

when all of the forces acting on an object are totalled.

If the net force is zero the forces are said to be balanced

If the net force if great in one direction, they are not balanced

Force, mass and acceleration 2

If the opposing forces are balanced there is no net movement

If one force is bigger than the other the object will move in that direction

Weight

Support

Drag/FrictionThrustThrust

Force mass and acceleration 3

The formula F=ma can be used to show the relationship between these things where:◦F = force (N)◦m = mass (kg)◦a = acceleration (ms-2)

The triangle can also be used to rearrange this formula

There are 2 patterns to remember:◦Greater force = greater acceleration◦Larger mass = smaller acceleration

Force, mass and acceleration problems

In the following situations the net force on the object is known. Write down the size of the forces A-D

Roger Federer can hit a tennis ball (0.057kg) so the ball accelerates at 224ms-1. Calculate the force the racquet exerts on the ball

A box is dragged across an icy surface with a force of 47N. It is accelerating at 0.08ms-1. Calculate the mass of the box

Mass, gravity and weight

Mass is the amount of matter an object hasGravity is the force pulling an object to another. On earth thisis approx. 10ms-2Weight is the effect of gravity on an object and is a force (N)

The formula to calculate weight is:◦Fw = mg (where g=10 on earth)

Friction

Friction is a force created when 2 surfaces move, or try to move across each other.

It opposes the movement of one object past another

Copy and complete the following paragraph:◦Friction is a ________ that is created when two ______ move

or try to move. Friction acts in the ______ direction to movement and depends on the ______ of the two surfaces. Friction can be useful eg ______ slow down a car, or not useful eg rubber wearing off a ____. Wheels reduce friction by ______ the areas in contact. The friction that prevents a stationary object from moving is _____ friction. The friction force or air is also known as _____.

Pressure

Pressure depends on two things◦Force applied◦Area being pushed on

The relationship is:

A force acting over a small area gives a larger pressure than the same force acting on a larger area

The trick with these questions is to make sure you look at the whole area (ie is there 1 shoe or 2, are there studs and how many)

Pressure question

The diagram below shows a pair of ski’s. Calculate the pressure exerted when Rosemary (60kg) stands upright on these ski’s

Energy 1

Energy is required to make anything happen or change

There are different forms of energy potential (stored) energy and other active forms:◦Heat◦Sound◦Solar ◦Kinetic (the energy of a moving object)◦Gravitational potential◦Elastic potential◦Chemical Potential

Energy 2

The law of conservation of energy states that: “energy cannot be created nor destroyed, merely changed

from one form to another”. This is an energy transformation and is usually shown as

below:

Chemical potential Elastic potential

Kinetic gravitational potential kinetic

Gravitational potential energy

The formula for this relationship is as follows:Ep = mgh

◦Ep is Potential energy◦m is mass◦g is gravity (10)◦h height (of object off ground)

A 900kg car is lifted 2m above a workshop floor. How much Gravitational potential energy does it have?◦Ep=mgh where m=900, g=10, h=2◦Ep = 900 x 10 x 2◦Ep = 18000J

Kinetic energy

The formula for the energy of a moving object is as follows:

Ek = ½mv2

◦Ek is energy in J◦m is mass in kg◦v is velocity in ms-1

A 1000kg speedboat is travelling at 16ms-1 How much energy does it have?◦Ek= ½mv2 where m=1000 v=16◦Ek = 0.5 x 1000 x 162

◦Ek = 128J

Potential energy into kinetic energy

Usually kinetic energy comes from potential energy

For some excellence level questions you have to calculate the amount of potential energy then use this figure to calculate the speed of an object by rearranging the formula

In this case you have to assume that all of the potential energy is converted to kinetic energy with none being lost

Potential energy into kinetic energy 2

Eg;A sack with a mass of 50kg is raised to a height or 5m above the ground and is allowed to fall.

◦What is the sacks gravitational potential energy before it is released?

◦How much speed does the sack have just before it hits the ground?

However we know that some of the energy is always lost as ______

Work

In order for energy to change from one form to another, work must be done.

The relationship for this is:W = Fd

◦W is work (J)◦F is force (N)◦d is distance (m)

This can also be put into the triangle as the formulae earlier in order to calculate any part of it

Work problems

Complete the following table:

Calculate the work done when a person uses a constant force of 25N to drag a box for a distance of 15m

You should be able to see that the amount of energy that is required to move that box will be the same

Situation Work done?

Reason

Someone climbs a stepladder

Yes Movement against the force of gravity

A child pulls a toy along the groundA crane exerts a force of 10000N on a container but does not move itA rock falls off a cliff and into the river

Yes

No

Yes

Movement against the main opposing force of friction of the floor

No movement

Work done in the change of Gravitational potential energy to kinetic energy

Power

Power is the rate at which work is done It uses the formula

Usually a question will ask you to compare two things and say which was more powerful and why

Two men were bench pressing 80kg (pushing the weights upwards from their chest as far as their arms could extend). One man’s arms were 0.65 m long and the other man’s were 0.60 m long. Both men took exactly 2.5 seconds to fully extend their arms.

The man with the longer arms said that he had to do more work than the man with the shorter arms but the man with the shorter arms was more powerful. Was he correct?