# Friction Check-up

In this worksheet, students will consolidate their understanding of friction and the factors which reduce or increase it.

Key stage:  KS 2

Curriculum topic:   Forces

Curriculum subtopic:   Resistance and Friction

Difficulty level:

### QUESTION 1 of 10

Friction - the force - acts all around us whenever surfaces rub together.

Friction can be useful, and it can also be very unhelpful.

Smooth surfaces and streamlined shapes reduce friction.

Rough surfaces and lumpy, awkward shapes increases friction.

Increasing the area of the surfaces which rub together also increases the size of the force.

In this worksheet you will be asked some questions on friction, let's see what you can remember!

So, thinking back to the introduction, which THREE variables increase friction?

surface area

streamlining

roughness

smoothness

'bumpy' (not smooth) shapes

Now choose THREE variables which increase air resistance?

speed

colour

rough surface

a flat front

a pointed front

Swimming is hard work - you, or this dolphin, have to push the water out of the way in order to move.

Which THREE variables reduce water resistance (remember, a dolphin has to swim fast)?

smooth surface

flippers

the weather

pointed front

streamlined shape

Ships and boats have smooth, painted sides (hulls) because......

it increases the friction

it reduces the friction

it camouflages them

Mammals which are adapted to living in the sea do not have arms and legs - they have been turned into flippers.

Which statement best describes why this is?

to help them breathe underwater

to create a smooth shape

to make their coats more shiny

When birds fly, they have to overcome air resistance.

In which THREE ways do they achieve this?

they have long beaks

they have smooth feathers

when they fly together, they fly in a 'V' shape

they always have the wind behind them.

they have a 'pointed' shape

Animals that live in water often have webbed feet because.......

they increase water resistance

they reduce water resistance

to make themselves easier to see in the water

Olympic cyclists wear a funny-shaped cycling helmet because.....

they are more comfortable

it increases friction

it reduces air resistance

Match up the statements below about these two different cycling sports: road cycling and mountain biking.

## Column B

knobbly, wide tyres
reduce friction with the ground
smooth narrow tyres
increase friction with the ground
tucked in arms
increases air resistance
loose fitting clothing
reduce air resistance

Racing bicycles and the clothing worn by racers are designed to...

increase friction

increase speed

keep the racer safe

• Question 1

So, thinking back to the introduction, which THREE variables increase friction?

surface area
roughness
'bumpy' (not smooth) shapes
EDDIE SAYS
Remember, friction is a force that slows down motion when surfaces rub against each other. So if the surface is rough = greater friction; if it's a large surface = more friction; if it's a bumpy surface = more friction. That's important if you need something to slow down or to 'grip' better - notice how "bumpy" a road surface is, so your bike tyres 'grip' it properly - that's high friction (and you wouldn't want it any other way!).
• Question 2

Now choose THREE variables which increase air resistance?

speed
rough surface
a flat front
EDDIE SAYS
The faster an object travels, the more the air pushes against the surface of the object, increasing the air resistance. So if the surface is rough and has a flat front, then there's even more friction. That's why you don't often see vans covered with grass - flat front and a 'bumpy' surface! They're not going to be fuel efficient, are they?
• Question 3

Swimming is hard work - you, or this dolphin, have to push the water out of the way in order to move.

Which THREE variables reduce water resistance (remember, a dolphin has to swim fast)?

smooth surface
pointed front
streamlined shape
EDDIE SAYS
Designers copy the shape of water-living animals in their designs because they have evolved to reduce the friction between themselves and the water around them. Dolphins are brilliant swimmers and are a pointy, streamlined shape with a really smooth skin - all help to push water out of the way more easily (using less energy). Flippers are there to provide the force to move and steer, but don't really affect friction in this way, while the weather doesn't make a lot of difference to the friction when you're beneath the surface.
• Question 4

Ships and boats have smooth, painted sides (hulls) because......

it reduces the friction
EDDIE SAYS
Just like a dolphin, the boat wants to move through the water easily - that uses less fuel. So having a smooth hull helps to achieve this by reducing the friction between the boat and the water.
• Question 5

Mammals which are adapted to living in the sea do not have arms and legs - they have been turned into flippers.

Which statement best describes why this is?

to create a smooth shape
EDDIE SAYS
The arms and legs of a sea-mammal's skeleton have evolved into flippers which gives their body a smooth 'torpedo-like' shape, allowing them to swim quickly without using lots of energy to overcome water resistance. The flippers themselves push strongly against the water and then are tucked alongside the body as the animal is propelled forward.
• Question 6

When birds fly, they have to overcome air resistance.

In which THREE ways do they achieve this?

they have smooth feathers
when they fly together, they fly in a 'V' shape
they have a 'pointed' shape
EDDIE SAYS
As you know, shape makes a massive difference: more pointy = less friction/resistance. That's also true of the surface: smooth = less friction. For birds that fly in a flock, like geese, they fly in a V formation as it helps the air to pass over the group more easily so that each goose, apart from the lead goose, creates less air resistance. That's why the lead goose is swapped over quite regularly - to get a rest!
• Question 7

Animals that live in water often have webbed feet because.......

they increase water resistance
EDDIE SAYS
The increased surface area increases the water resistance, but means that the animals can push against the water which makes them move forward. The larger area of the webbed foot gives a bigger 'push' than, say, a hand or a paw. Then it's often tucked in against the side of the body as the animal moves forward through the water.
• Question 8

Olympic cyclists wear a funny-shaped cycling helmet because.....

it reduces air resistance
EDDIE SAYS
Cyclists' clothing (and bicycles) are designed to reduce air resistance. The smooth surface and streamlined shape all help. Remember - we may not be the fastest people on two wheels, but cycle helmets PROTECT us if we fall off!
• Question 9

Match up the statements below about these two different cycling sports: road cycling and mountain biking.

## Column B

knobbly, wide tyres
increase friction with the ground
smooth narrow tyres
reduce friction with the ground
tucked in arms
reduce air resistance
loose fitting clothing
increases air resistance
EDDIE SAYS
You're getting the idea! Road racers need to minimise friction so have narrow tyres and tucked-in arms to reduce air resistance. Meanwhile, mountain bikers want a lot of 'grip' to stay on the loose surface they're cycling on, so they have knobbly tyres on their bike and loose clothing to increase the resistance with ground and air.
• Question 10

Racing bicycles and the clothing worn by racers are designed to...

increase speed
EDDIE SAYS
Racing bikes and 'skin-suits' worn by cyclists are designed to reduce the friction around them helping them to go really fast! Smooth surface, streamlined shape - make sense?
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