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Understand Newton's First Law

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

Worksheet Overview

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 as a force. Not only that, he also changed our perception of light, maths and motion, as well as 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 lectures to empty lecture halls because he had annoyed everyone who was meant to turn up. He once wrote a book which changed the way we look at the world, but he 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 himself, 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 burned all of his portraits, so we have no idea what Hooke looked like! So let's look at some of the science that Newton discovered.  In this activity, we will be looking at Newton's First Law and we will use it to describe the motion of objects.

 

So, here 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 comes and applies a force to it (for example if you push 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 push it again. 

 

There has to be a force applied 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 going at top speed. The lights turn green and you floor the accelerator. The car lurches forward really fast - there is an acceleration. This means that there must be a force provided by the car pushing it forward. As the car gets faster and faster, it starts to pick up more and more resistance from the air and the road. This begins 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

 

That's it! Let's have a go at some questions on this now.

In which of these situations are the forces balanced.  

A car driving at a constant speed

A person who has just jumped out of a plane

A gymnast jumping on a springboard

Usain Bolt on the starting line before the gun goes off

A car braking to try and avoid a crash

You sitting on your sofa at home

Michael Jordan jumping from the free throw line to dunk

What must happen to forces if an object needs to accelerate?

They need to be balanced

The force in the direction of travel needs to be bigger

The force opposite to the direction of travel needs to be bigger

A force upwards needs to exist

What does the term 'terminal velocity' mean?  

 

[1]

Describe the forces on an object dropped from the Empire State Building, in the first few seconds.  

 

[2]

In order to reach terminal velocity, two forces need to be balanced.

 

Select the two forces from the list below necessary 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 it?

Upthrust

Air resistance

Buoyancy

Gravity

Friction

Drag

A feather and a hammer were dropped on the moon during the Apollo 15 mission. They fell and hit the ground at the same time because there is no air resistance on the moon. 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]

What does the term velocity mean?

Speed

Distance

Speed in a direction

Distance in a direction

A car needs to accelerate.

 

Describe the forces required to make this acceleration happen.   

 

[2[

Match the forces with the situation.

Column A

Column B

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

In which of these situations are the forces balanced.  

CORRECT ANSWER
A car driving at a constant speed
Usain Bolt on the starting line before the gun goes off
You sitting on your sofa at home
EDDIE SAYS
There were three correct answers this time. Did you get all of them? Forces are balanced when you have an object that is moving at a constant speed or not moving at all. In two of the correct options above, there is no movement and in the other one, the car is moving at a steady speed and not accelerating or slowing down. In the other four incorrect options, there is a change in the speed of the movement.
  • Question 2

What must happen to forces if an object needs to accelerate?

CORRECT ANSWER
The force in the direction of travel needs to be bigger
EDDIE SAYS
If you think about it, it's 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 increase the force in the direction that it is moving. Does that make sense?
  • Question 3

What does the term 'terminal velocity' mean?  

 

[1]

CORRECT ANSWER
EDDIE SAYS
Terminal velocity is about the forces acting on an object. It's when it can't be accelerated any more because the forces have become balanced. This happens at the object's maximum speed because it can't be accelerated, which means that 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 using the word 'forces' would have been more accurate.
  • Question 4

Describe the forces on an object dropped from the Empire State Building, in the first few seconds.  

 

[2]

CORRECT ANSWER
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! This was worth two 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 produce an 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 necessary for a falling object to reach terminal velocity. 

CORRECT ANSWER
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 to make sense of what is going on. Now picture it in your mind, can you see any water? No? Everything to do with water is out. Now, what are we told about the object? We know that it is falling so, what is pulling the object down? Gravity? Good! Now, what is going to be pushing the object back up? That's air. It's the only thing that can push it up, so the other answer needs to be something to do with the air. Drag. Great detective work here!
  • Question 6

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

CORRECT ANSWER
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. 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 going to remain stationary!
  • Question 7

A feather and a hammer were dropped on the moon during the Apollo 15 mission. They fell and hit the ground at the same time because there is no air resistance on the moon. 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]

CORRECT ANSWER
EDDIE SAYS
This question was about two 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). 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). Well done for completing another challenging activity!
  • Question 8

What does the term velocity mean?

CORRECT ANSWER
Speed in a direction
EDDIE SAYS
Now, did you fall into the trap and go for 'speed' here? It's easily done but very important that you understand the difference between those two words. Velocity is one of those vectors we talked so much about in forces - but it's going to come up a lot here too. A vector (if you remember) is a unit and a direction. So, distance and direction is the vector displacement. Speed and a direction is the vector velocity.
  • Question 9

A car needs to accelerate.

 

Describe the forces required to make this acceleration happen.   

 

[2[

CORRECT ANSWER
EDDIE SAYS
A nice simple 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 acceleration and asking you to describe what is going on with the forces. You need a bigger force in the direction of the acceleration.
  • Question 10

Match the forces with the situation.

CORRECT ANSWER

Column A

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! It does look pretty challenging as a question but just work through each one carefully. It's quite simple if you picture what is going on and then try to match it up in your imagination. The only thing you need to watch out for is the word resultant force - which means the total force.
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