# Showing Forces 1

In this worksheet, students will be helped to look at forces visually, using visual cues to encourage understanding of the size and direction of different forces and how a particular object behaves in relation to those forces.

Key stage:  KS 3

Curriculum topic:   Physics: Motion and Forces

Curriculum subtopic:   Motion and Forces

Difficulty level:

### QUESTION 1 of 10

One way in which forces can be represented is by using labelled arrows; for example here's someone swimming:

As you can see, he propels himself through the water using his arms and legs, pushing the water out of the way, which creates RESISTANCE to the forward motion in the form of friction.

These forces are represented by a THRUST arrow as the swimmer pushes himself forward and then a FRICTION arrow acting in the opposite direction, pushing against the swimmer.

Notice that the THRUST arrow is bigger than the FRICTION arrow, meaning that the swimmer must be speeding up as he is overcoming the water resistance acting against him. If the two arrows were the same size, the forces would be equal, so he would be moving at a steady speed.

OK, use this idea in the questions on this worksheet.

Here is a plane flying along at a steady speed:

There are three arrows shown representing different forces.

Match each arrow to the correct force.

## Column B

A
Thrust
B
Friction
C
Gravity

Here is a picture of a car driving along:

It has TWO force arrows acting against it.

What forces do you think these two arrows represent (tick two you think are right)?

air resistance

gravity

light resistance

If the driver now applies the brakes which of these three pictures would be the correct representation of how the forces change?

A

B

C

Here is a skydiver falling at a steady speed through the air:

Which force does arrow B represent?

Friction

Gravity

Falling

When the skydiver pulls the parachute cord, this is what happens:

Which force has increased?

Gravity

Friction

Pulling Upwards

Billy likes painting his Warhammer figures - here's one he's finished:

He hangs his figure on a forcemeter to see how much it weighs:

Which force acting on his figure is Billy measuring?

Gravity

Friction

Stretching

His figure weighs 0.5N.

Keeping it on the forcemeter he lowers the figure into a glass of water and to his surprise he finds the reading decreases to 0.4N.

What is the name of the force that causes his figure to seem to weigh less?

Water Pressure

Upthrust

Friction

Next Billy replaces his Warhammer figure with a rubber ball to see how much that weighs on his forcemeter. He finds the answer is 5N.

When he lowers the ball into a tub of water he finds that the ball floats.

What do you think is the likely reading on his forcemeter when the ball is floating?

0N

1N

5N

Here is a picture of Billy's ball floating in the water:

Which force does arrow A represent?

Upthrust

Billy pushing

Gravity

Here again is a picture of Billy's ball floating in the water:

The arrows are drawn in opposite directions but they are the same size. What do you think this means?

the ball is being squashed

the ball is stationary at that level in the water

the ball is moving sideways in the water

• Question 1

Here is a plane flying along at a steady speed:

There are three arrows shown representing different forces.

Match each arrow to the correct force.

## Column B

A
Friction
B
Gravity
C
Thrust
EDDIE SAYS
Gravity, of course, always acts downwards (B) and the thrust of the engines is pushing the plane forward (C). It has to push the air out of the way: that's air resistance or friction (A).
• Question 2

Here is a picture of a car driving along:

It has TWO force arrows acting against it.

What forces do you think these two arrows represent (tick two you think are right)?

air resistance
EDDIE SAYS
When a car is driving along the tyres rub against the road (=friction) and the air pushes against the car. Both of these forces need to be overcome for the car to speed up.
• Question 3

If the driver now applies the brakes which of these three pictures would be the correct representation of how the forces change?

A
EDDIE SAYS
Pic A shows one of the friction forces acting against the car increasing - that's the brakes slowing the car down. Pic B actually shows the car speeding up (more thrust) and Pic C shows air resistance increasing as well as braking (which it wouldn't) and gravity isn't acting downwards!
• Question 4

Here is a skydiver falling at a steady speed through the air:

Which force does arrow B represent?

Gravity
EDDIE SAYS
What pulls the skydiver down ....? Gravity! So that's the force acting downwards, with friction acting against the skydiver.
• Question 5

When the skydiver pulls the parachute cord, this is what happens:

Which force has increased?

Friction
EDDIE SAYS
By opening the parachute there is now a massive area to "catch the air", meaning that the air resistance increases a great deal; in other words, the friction due to the air is much greater, slowing the skydiver down so that they reach the ground safely.
• Question 6

Billy likes painting his Warhammer figures - here's one he's finished:

He hangs his figure on a forcemeter to see how much it weighs:

Which force acting on his figure is Billy measuring?

Gravity
EDDIE SAYS
When you measure how 'heavy' something is (or weigh it) you're measuring the pull of gravity on that object.
• Question 7

His figure weighs 0.5N.

Keeping it on the forcemeter he lowers the figure into a glass of water and to his surprise he finds the reading decreases to 0.4N.

What is the name of the force that causes his figure to seem to weigh less?

Upthrust
EDDIE SAYS
Basically water pushes UP against the force of gravity: gravity still acts through water, of course, but the support that water gives (because it's much 'thicker' than air) means that this upthrust causes objects to weigh less in water than air. Marine animals can grow much bigger because of this: the blue whale is the biggest animal EVER to have lived on earth!
• Question 8

Next Billy replaces his Warhammer figure with a rubber ball to see how much that weighs on his forcemeter. He finds the answer is 5N.

When he lowers the ball into a tub of water he finds that the ball floats.

What do you think is the likely reading on his forcemeter when the ball is floating?

0N
EDDIE SAYS
When an object floats the upthrust has overcome gravity and although gravity is keeping it on the surface of the water the upward force of the water means that it has no weight in water due to gravity as the upthrust force is greater.
• Question 9

Here is a picture of Billy's ball floating in the water:

Which force does arrow A represent?

Gravity
EDDIE SAYS
The downward arrow represents the pull of gravity on the ball which, even though it floats, is being kept in the water by gravity.
• Question 10

Here again is a picture of Billy's ball floating in the water:

The arrows are drawn in opposite directions but they are the same size. What do you think this means?

the ball is stationary at that level in the water
EDDIE SAYS
Force arrows that are equal and opposite mean either: a)the object is not moving or b) it is moving at a steady speed, not slowing down or speeding up. Since the ball is steady in the water it means it's simply sitting still.
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