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Physical Science
Grade5, Unit5P.3: Friction
Unit 5P.3: Friction
• Friction • Air resistance • Water resistance
Science skills: • Estimating • Measuring
the end of this unit you should:By • Know that friction is a force that opposes
movement.
• Know that water and air resistance slow an
object when it moves through them.
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Physical Science
Grade5, Unit5P.3: Friction
Friction Friction occurs when two surfaces are in contact with each other. Rougher surfaces produce a lot of friction and smooth surfaces produce less friction. • Rougher surfaces SLOW things down. Roads are rough to help you slow down quickly if you have to. • Smooth surfaces DO NOT slow you down. • Friction produces HEAT.
Friction is a force that stops things from moving or causes
them to move more slowly.
Friction always acts in the direction which opposes the motion.
5.12.1, 5.12.3
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Physical Science
Grade5, Unit5P.3: Friction
Activity: Best surface Why do some things slide more easily than others? You will need
• A large wooden board • A smooth plastic tray • An assortment of flat-bottomed objects that won't
break easily, like a plastic cup, coin, rubber, matchbox.
Project
1-Rub your hands together. 2-Add soap and water and rub them together again.
Which movement is easier with soap, or without soap?
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Explain your answer.
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1. Line your objects along one end of the wooden board. 2. Predict which one you think will slide the easiest._________________
2. Slowly lift the end of the board and find out which one slips the easiest, and which sticks the most. Repeat to make sure you are correct.
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Physical Science
Grade5, Unit5P.3: Friction
My observation:-------------------------------------
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This quick activity shows that the amount of friction between
two surfaces depends on how rough or smooth they are.
What's going on?
Some things slide along the wooden board more easily than
others because there is less friction between their bottom
surface and the board. They will probably be the objects
that feel smoother to the touch. Things slide much more
easily along a smooth surface like the plastic tray for the
same reason.
Lubrication:
A lubricant is a substance introduced to UreduceU 0Tfriction 0T
between moving surfaces, making the object move easily.
3. Now try using the plastic tray.
Does it make a difference?
---------------------------
How? ______________________________________
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Physical Science
Grade5, Unit5P.3: Friction
There are two types of lubricants:
ULiquidU: such as grease or oil
USolidU:
• such as bearings or rollers.
• Graphite – which is powdered carbon
the same as your pencil.
Types of friction:
There are two types of friction:
1U. Static friction: U
This type of friction happens, when an object Udoes not move. U U2. Dynamic friction: This type of friction happens, when an Uobject is moving U.
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Physical Science
Grade5, Unit5P.3: Friction
Stopping cars: After looking at this graph, please answer the question: Which is the best surface to put at the bottom of a ramp for stopping cars? ----------------------------------------------
Useful Friction
Have you ever tried riding a bicycle which has oil on its
brake pads? Do you think it is safe or dangerous thing to do?
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Examples of useful friction:
- Shoe soles
- Brake pads
Sand is the best surface for stopping cars and this is because of the high friction of the sand. Look the picture, they have sand in the ‘pit stop’ area where racing cars need to slow down very quickly.
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Physical Science
Grade5, Unit5P.3: Friction
- Car tires
- Car clutch plates
- Shock absorber in a car.
- Goal keeper’s gloves.
Key Words:
- Friction - Surface - Rough - Smooth - Dynamic - Static
Key Ideas
• Friction is a force that opposes movement. • The nature of surfaces in contact influences the size of
the frictional force. • Dynamic friction: during the movement of an object. • Static friction: acting when an object does not move.
Project: Design and carry out an investigation to discover
how the area of the bottom of a box affects the size of
the frictional force between the box and the surface.
The variables will be the area of the box and the force
needed, while the nature of the surface and the mass of
the box contents should be controlled.
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Physical Science
Grade5, Unit5P.3: Friction
Key Questions 1. In which direction does friction always act?
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2. Name two situations where friction is helpful?
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3. Usama and Umar are wearing shoes with rubber soles.
They both have the same size feet. Why does a boot
with a good grip help when you walk on a slippery
surface?
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Usama’s shoes Umar’s shoes
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Physical Science
Grade5, Unit5P.3: Friction
Air Resistance
Have you ever cycled really fast down a hill?
You can feel the air pushing against you.
This air pushing against you is the Air resistance.
It is the force of the air against any moving object.
The bigger the surface area is moving into the air, the
bigger the air resistance.
When you bend down over the handlebars of a bike you make
your surface area smaller, and so the air resistance is less.
When an object moves through the air it experiences
frictional forces.
These frictional forces are called air resistance.
The faster the object moves the larger air resistance.
Air resistance is the force of the air against any moving object.
5.12.4
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Physical Science
Grade5, Unit5P.3: Friction
How to travel faster?
Air slows you down. To travel faster through air, objects
need to have a streamlined shape.
To travel slower through air, you need a large surface area
(like a parachute).
Air resistance
Gravity
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Physical Science
Grade5, Unit5P.3: Friction
Cars that break world speed records are very streamlined
but when it is time to stop, they dramatically increase the
air resistance by releasing a parachute behind them.
Activity 1: Dropping paper You will need Write down what do you think will happen if you drop two pieces of paper. * The same size * From the same height * At the same time * One piece crumpled and the other piece flat Now try What happened?
........................................................
Was your prediction correct?
......................................................................
Explain your answer
……………..............................................................
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Physical Science
Grade5, Unit5P.3: Friction
Activity 2: Falling parachutes Here are some ideas, read them carefully, then answer below.
1. Which is the best explanation? Why?
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2. What properties should a parachute material have?
---------------------------------
---------------------------------
3. How do these properties help the
parachute work?
---------------------------------
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1. Parachutes work because of air resistance or air friction over the surface or the parachute. 2. Real parachutes are so big that the person comes down slowly. 3. It is because of air resistance. 4. Air holds the parachute up so that it floats down.
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Physical Science
Grade5, Unit5P.3: Friction
Parachute Problems
We wanted to find out if the Usize U of a parachute affects how long it takes to fall? We needed:
• paperclips • thread • plastic bags • scissors • sellotape
We made five parachutes each with a different sized canopy. To make the test fair we made sure that Uthe weight it was carrying and the distance it fell was the same each time. We tested our parachutes by:
______________________________________ Our results: Parachute description: Time to fall: Conclusion:
The __________________ parachute fell the fastest. The __________________ parachute fell the slowest. This shows that ______________________________ __________________________________________
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Physical Science
Grade5, Unit5P.3: Friction
Parachute Problems We wanted to find out if the Ushape U of a parachute affects how long it takes to fall? We needed:
• paperclips • thread • plastic bags • scissors • sellotape
We made five parachutes each with a different shaped canopy. To make the test fair we made sure Uthat the surface area and the weight it was carrying was the same each time. We tested our parachutes by:
______________________________________ Our results: Parachute description: Time to fall: Conclusion:
Our results show that _________________________ __________________________________________ __________________________________________
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Physical Science
Grade5, Unit5P.3: Friction
Key Words:
• Air
resistance
• Streamlined
• Parachute
Key Ideas • Know that air resistance slows an
object down when it moves through air.
• The shape of an object affects the
size of air resistance.
Key Question
1. What is the shape of this bird?
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2. Write how this shape helps the bird to fly.
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3. Some of these vehicles have been streamlined to reduce air
resistance. Tick the one from each pair which will produce the
least air resistance:
4. Why is reducing air resistance a good idea for trains, cars,
boats and planes? ------------------------------------------------
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Physical Science
Grade5, Unit5P.3: Friction
Water resistance When an object sinks through water, it is slowed by the
water pushing against it. This is called water resistance.
Different shapes have different resistance in water.
Have you ever tried walking through the sea or a swimming
pool? Not easy, is it? The water pushes back on you. This is
called water resistance. Like friction, it can nearly stop you
from going forward.
Some shapes will travel through water much more easily than
others.
The best shape to reduce the water resistance is the
streamlined shape.
Water resistance is force acting against an object moving in water.
5.12.4
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Physical Science
Grade5, Unit5P.3: Friction
What do you think about the shapes of these boats and
animals? What do these shapes have in common?
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Activity
Best shape under water
A TV company called Underwater World wants help with a problem. They are making a new series of films about sea life. They need a new diving vessel to travel very quickly through the water as fast as possible. Use plasticizers to model four shapes. 1. Predict which shape will move quickest through the water.
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2. Make your shapes one at a time, release them in the
water and time how long they take to reach the bottom.
Remember to use the same piece of plasticizer each time and
start from the same place or your test won't be fair.
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Physical Science
Grade5, Unit5P.3: Friction
Time needed to reach the bottom
Shape
3. Which shape traveled fastest? Was it the one you
predicted?
-------------------------------------------- -------------------------------------------- Applications of water and air resistance:
Water resistance Air resistance Swimming PPaarraacchhuutteess // PPaarraagglliiddiinngg Diving KKiittee--ffllyyiinngg Boat Sailing WWiinnddmmiillllss ((aass aa rreenneewwaabbllee
ssoouurrccee ooff eenneerrggyy)) Water sports FFllyyiinngg ((bbiirrddss,, ppllaanneess))
Key Words:
• Water resistance
• Streamlined
Key Ideas • Know that water resistance slows
an object down when it moves
through water.
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Physical Science
Grade5, Unit5P.3: Friction
Key Question
1. What is the best shape to move in water?
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2. If two objects have the same mass will they both
float?
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Why?
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3. Which items do you think will float and why?
Objects Will it float? Why?
Rubber duck
Egg
Brick
Pencil
Boat
