# Understand Newton's First Law

In this worksheet, students will understand the principles of Newton's first law of motion and apply it to different situations including free-fall.

Key stage:  KS 4

GCSE Boards:   AQA Trilogy, AQA, AQA Synergy, OCR Gateway, Pearson Edexcel, Eduqas

Curriculum topic:   Forces, Movement and Interactions, Motion and Forces, Forces and Motion

Difficulty level:

### QUESTION 1 of 10

Just so you know - you should have a good understanding of forces before starting this worksheet.

Newton was one of the most amazing people who has ever lived. He completely changed our understanding of gravity (discovering it as a force), light, maths, and motion as well as basically creating the scientific method (along with Galileo and some of his friends). He really was one of the smartest people who ever lived, and no one liked him. He was not a popular person at all! He used to give full lectures to empty lecture halls because he had annoyed everyone who was meant to turn up. He once wrote a book (it was amazing, and changed the way we look at the world) but didn’t get it published for years after he had finished it because he didn’t think there was anyone in the world apart from his smart enough to understand it. He got into a fight with a scientist called Hooke (also quite an amazing person), and when Hooke died, Newton burnt all of his portraits, so we have no idea what Hooke looked like! So, let's study the science that this monster made! In this activity, we will be looking at Newton's First Law and we will use it to describe the motion of objects.

So, what is Newton's first law – ‘An object will have a constant velocity unless it is acted on by an outside force’

Remember this! It is important.

But let’s take a look at what it actually means. It’s really simple, let’s use a teddy as an example! If the teddy is not moving, then it won’t move (obviously). If something, then comes and applies a force to it (for example if you punch it) then it will start to move. If you did this in space where there is no friction, then the teddy would continue to move forever, but on the earth, there is the force of friction that slows the bear down until it stops. Then it won’t move until you punch it again.

Basically – there has to be a force for an object to accelerate or decelerate – otherwise, it won’t move or it will keep on moving at the same speed.

Let’s look at someone in a drag race to top speed. The lights turn green and you floor the gas pedal. The car lurches forward really fast - there is an acceleration. This means that there must be a force provided by the car pushing the car forward. As the car gets faster and faster it starts to pick up more and more resistance from the air and the road. This starts to slow down the acceleration of the car as the forces become more and more balanced. When they are balanced again, the car has reached its maximum speed and there is no more force to accelerate it anymore – this is called its terminal velocity.

We can draw this in a free body diagram over multiple stages and it might look like this:

IMAGE OF FREE BODY DIAGRAM OF CAR

In which of these situations are the forces balanced. Tick all of the boxes that apply.

A car driving at a constant speed

A person who has just jumped out of a plane.

A formula 1 car after the lights have just gone out.

Usain Bolt on the staritng line before the gus goes off.

A car breaking to try and aciod a crash.

You sat on your sofa at home.

Michael Jordan jumping from the free throw line to dunk.

If an object needs to accelerate, what needs to happen to for forces?

They need to be balanced

The force in the direction of travel needs to be bigger

They force opposite the direction of travel needs to be bigger.

A force upwards needs to exist.

What does the term 'terminal velocity' mean?

Describe the forces on an object dropped from the empire state building in the first few seconds (2 marks)

In order to reach terminal velocity, two forces need to be balanced. Select the two forces from the list below for a falling object to reach terminal velocity.

Upthrust

Air resistance

Buoyancy

Gravity

Friction

Drag

If an object is stationary and there are no other forces acting on it, what will happen to the object?

A feather and a hammer were dropped on the moon during the Apollo 15 mission. The fell and hit the ground at the same time because there is no air resistance on the moon. but if you try this same experiment on the earth there will be quite a long time between the hammer hitting the ground and the feather hitting the ground. Using the idea of terminal velocity, explain why. (4 marks)

What does the term velocity mean?

Speed.

Distance.

Speed in a direction.

Disance in a direction.

A car wants to accelerate. Describe the forces requiered to make this acceleration happen. (2 marks)

Match the forces with the situation.

## Column B

No resultant force on a stationary object.
No acceleration.
Resultant force to the left
Continues to move at a constant speed.
Resultant force to the right
Acceleration to the right
10 N left and 10 N right
Acceleration to the left.
No resultant force on a moving object
No movement
• Question 1

In which of these situations are the forces balanced. Tick all of the boxes that apply.

A car driving at a constant speed
Usain Bolt on the staritng line before the gus goes off.
You sat on your sofa at home.
EDDIE SAYS
EXAM TIP - These questions that say 'tick all of the boxes that apply' normally mean 3 or more boxes. They will only be worth 2 marks, but don't let that fool you - there will be more than 2 boxes to tick! Just read through them all ad tick all of the boxes that you think are correct! For this question, the forces are balanced when you have an object that is moving at a constant speed or not moving. Did you find all of the answers where that was the case?
• Question 2

If an object needs to accelerate, what needs to happen to for forces?

The force in the direction of travel needs to be bigger
EDDIE SAYS
If you think about it, it is obvious. When you are given problems like this, think about what is actually happening in real life and what you would have to do to get the same result. If you want an object to start moving - you have to push it, and you have to push it in the direction that it needs to travel. So you need to make the force in the direction that it is moving bigger, right?
• Question 3

What does the term 'terminal velocity' mean?

EDDIE SAYS
Terminal velocity is about the forces acting on an object. It is when it cannot be accelerated any more because the forces have become balanced. This happens at the objects maximum speed (because it can't be accelerated so the pushing forces are the same as the forces that are pushing the object back). In this case, you could have written maximum speed or spoken about the forces, but forces are the more correct answer.
• Question 4

Describe the forces on an object dropped from the empire state building in the first few seconds (2 marks)

EDDIE SAYS
Some points before we begin here. Did you get the directions for the force and the acceleration? Remember, they are BOTH vector values and so they need a direction attached to them! So this was worth 2 marks, and so you would get the first mark for saying that the forces are unbalanced - or there is a bigger force downwards (or something like that) and then the second mark was for saying that this would cause and acceleration towards the ground. DID YOU KNOW - that if you dropped a penny from the top of the empire state building, it would never reach a high enough speed to cause any damage to a person at the bottom. Its terminal velocity is surprisingly low (only about 13 m/s).
• Question 5

In order to reach terminal velocity, two forces need to be balanced. Select the two forces from the list below for a falling object to reach terminal velocity.

Gravity
Drag
EDDIE SAYS
For this type of question, the best thing to do is to picture what is happening in your mind - draw a picture if you think it will help you! When you do this, it really helps your brain make sense of what is going on (seriously, the best advice I give to A-Level students is draw a picture). Now picture it in your mind, can you see any water? No? Everything to do with water is out. What is pulling the object down? Gravity? Good! Now, what is going to be pushing the object back up? That air, right? It's the only thing that can push it up, so the other answer needs to be something to do with the air. Drag. DONE!
• Question 6

If an object is stationary and there are no other forces acting on it, what will happen to the object?

Remain stationary
Stay still
Sat stationary
EDDIE SAYS
Will it move if it doesn't have a force acting on it? The only way to accelerate an object is to give it an unbalanced force, right? So, will this object start to accelerate if there is no force acting on it? Of course not - it is dead in the water and is only gonig to remain stationary!
• Question 7

A feather and a hammer were dropped on the moon during the Apollo 15 mission. The fell and hit the ground at the same time because there is no air resistance on the moon. but if you try this same experiment on the earth there will be quite a long time between the hammer hitting the ground and the feather hitting the ground. Using the idea of terminal velocity, explain why. (4 marks)

EDDIE SAYS
This question was about 2 things - terminal velocity and how forces can affect terminal velocity. So - for a falling object to reach terminal velocity, the force pulling it down needs to be the same as the one pushing it back up. The feather is very light, so it will only get a small force pulling it down (its weight). The hammer is much heavier so it will have a bigger force pulling it down (its weight). The only force pushing the object back up is the air resistance (or drag). But this means that the feather doesn't need as much air resistance because it is much lighter. This means that the forces will become balanced much more quickly for the feather, reaching a much lower terminal velocity than the hammer. Boom! (the sound that the hammer makes when it hits the ground).
• Question 8

What does the term velocity mean?

Speed in a direction.
EDDIE SAYS
Velocity is one of those vectors we talked so much about in forces - but it is gonig to come up a lot here too, so we thought we\'d test you on it again. Aren\'t we mean! A vector (if you remember) is a unit and a direction. So distance and a direction is the vector displacement. Speed and a direction is the vector velocity.
• Question 9

A car wants to accelerate. Describe the forces requiered to make this acceleration happen. (2 marks)

EDDIE SAYS
A nice simple describe question here! It is testing you to see if you know that unbalanced forces create an acceleration, but it has flipped it. This time it is giving you a situation that needs an accelerating and asking you to describe what is gonig on with the forces. You need a bigger force in the direction of the acceleration BTW.
• Question 10

Match the forces with the situation.

## Column B

No resultant force on a stationar...
No movement
Resultant force to the left
Acceleration to the left.
Resultant force to the right
Acceleration to the right
10 N left and 10 N right
No acceleration.
No resultant force on a moving ob...
Continues to move at a constant s...
EDDIE SAYS
These are checking that you understand the different situations that a force can get you into! Oh, those cheeky forces... It is quite simple if you picture what is going on and then try to match it up to your imagination. The only thing you need to watch out for is the word resultant force - which you should know means the total force.