# Understanding Newton's Second law

In this worksheet, students will use the equation F=ma to understanding Newton's Second law and apply that to objects.

Key stage:  KS 4

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

Difficulty level:

### QUESTION 1 of 10

Just a quick note, this is Newton's second law, and it will help if you have a good understanding of Newton's first law before you start this. You might also want to refresh your understanding of acceleration as well. Also – we will not be covering the experiment related to newtons second law in this worksheet, for a detailed description of that, take a look at our activity called Investigating Motion. Notes all done now!

Ever tried to push a car? It’s difficult, right? Why? Because the car is heavy, or because gravity is pulling the car down, or because you have the hand brake on? Only one of these effects how difficult it is to push the car in a straight line, and that is the hand brake. If you think about it, gravity is pulling the car down, so why would that make it difficult to push along?

Okay, so you release the hand brake and try again, but it is still difficult to push along. Much more difficult than pushing a table, and a table doesn’t even have wheels! Why? What makes pushing a car hard? This is what we are going to be looking at in this activity. We will be looking at Newtons Second law, defining it and then using it to explain some everyday situations (like trying to push a car…).

Okay, so what is Newtons Second law? It says ‘The acceleration of an object is proportional to the force of an object’ this means that as the force goes up so does the acceleration. This makes sense, right? If up lightly push a pen on the table it won’t reach a very high top speed, but if you throw it with a lot of force then it will reach a much higher top speed.

Newton also said that ‘The acceleration of an object is inversely proportional to the mass of an object’. This is where the magic happened. What he was saying was as you increase the mass of an object, then you decrease the acceleration. So, a more massive object will accelerate slower than a less massive one. This is our car problem – because the car has a lot of mass it accelerates a lot slower. Newton called this idea inertia; it is the idea that the heavier object takes more force to accelerate them.

He went one step further though - he also made an equation with force acceleration and mass in it.

INSERT IMAGE OF EQUATION HERE

F = force (Newtons (N))
m = mass (Kilograms (kg))
a = acceleration (Meters per second per second (m/s/s))

So, let's look at an example together.

Q – A person is attempting to push a car to get it to accelerate at 2 m/s/s. The car has a mass of 900 kg. Calculate the force that will be needed by the person to achieve this acceleration.

Step 1 – highlight the numbers in the question.
A person is attempting to push a car to get it to accelerate at 2 m/s/s. The car has a mass of 900 kg. Calculate the force that will be needed by the person to achieve this acceleration.

Step 2 – write out the numbers
F = ?
m = 900 kg
a = 2 m/s/s

Step 3 – Put them into the equation

F = 900 x 2

F = 1800 N

Match the symbol to the unit below.

## Column B

Force (F)
Newton (N)
Mass (m)
Meters per second per second (m/s2)
Acceleration (a)
Kilogram (kg)

What is required to cause an acceleration?

Is force a scaler or a vector value?

Scaler

Vector

Newton's third law states that 'Acceleration is proportional to...' Fill in the blanks.

Acceleration

Mass

Force

Heat

Newtons' third law states 'Acceleration is inversely proportional to...' Fill in the balnks

Acceleration

Mass

Force

Heat

An object with a mass of 60 kg is accelerated at 0.5 m/s2. Calculate the force that the object was accelerated with.

An F1 car has an acceleration of 25 m/s2 and a minimum mass of 740 kg. Calculate the force provided by the engine of the F1 car.

When jumping out of a plane you will reach a top speed on your decent. Choose the correct name for that top speed for the list below.

Starting veloctiy

Ending velocity

Incredable velocity

Terminal velocity

When falling out of a plane, you will initially accelerate at 9.8 m/s2. The average person has a mass of 60 kg. Calculate the force that earth is applying to that person in order to get them to accelerate at 9.8 m/s2

In your own words, explain what Newtons Third Law is. (2 marks)

• Question 1

Match the symbol to the unit below.

## Column B

Force (F)
Newton (N)
Mass (m)
Kilogram (kg)
Acceleration (a)
Meters per second per second (m/s...
EDDIE SAYS
As always, knowing the units will help you to spot the correct numbers in the question which will, in turn, make it easier for you to solve the equation. It is also handy if it comes to actually putting the units into the equation! Just do it!
• Question 2

What is required to cause an acceleration?

Force
A force
EDDIE SAYS
Think about the teddy and its doomed adventure in showing you what a force is. If you hit it then it will move, but if leave it alone then it will stay where it is. It needs a force to act upon it before it is able to accelerate in any direction - the same is true about all objects, they all need a force to act on them before they are able to move.
• Question 3

Is force a scaler or a vector value?

Vector
EDDIE SAYS
What's this? A question from a few activities ago? Is this even allowed? Yes, yes it is because we make the rules. Also, because your understanding of forces relies on you know this kind of information. Scaler - without a direction Vector - with a direction. Force needs a direction and so it is a vector value.
• Question 4

Newton's third law states that 'Acceleration is proportional to...' Fill in the blanks.

Force
EDDIE SAYS
Acceleration is proportional to the force of an object. You hit the teddy with more force, it is going to go further. If you hit it with less force then it won't go as far. Remember - proportional means as one thing goes up then the other thing goes up as well.
• Question 5

Newtons' third law states 'Acceleration is inversely proportional to...' Fill in the balnks

Mass
EDDIE SAYS
This time we are looking for something that will go down when the acceleration goes up. If you think about the car example, the less mass the car has the easier it is to accelerate (that's why F1 cars are so light) so the lower the mass the easier an object is to accelerate! Amazing, right?
• Question 6

An object with a mass of 60 kg is accelerated at 0.5 m/s2. Calculate the force that the object was accelerated with.

30
EDDIE SAYS
This question is simple if you can remember the equation. F = ma F = ? m = 60 kg a = 0.5 m/s2 F = 60 x 0.5 F = 30 N
• Question 7

An F1 car has an acceleration of 25 m/s2 and a minimum mass of 740 kg. Calculate the force provided by the engine of the F1 car.

18500
18,500
EDDIE SAYS
Again a simple one if you can remember the equation: F = ma F = ? m = 740 kg a = 25 m/s2 F = 740 x 25 F = 18,500 N Done!
• Question 8

When jumping out of a plane you will reach a top speed on your decent. Choose the correct name for that top speed for the list below.

EDDIE SAYS
Think about the word terminal - you might have heard it before. If you are in a terminal at an airport or a bus terminal. The word terminal tends to be around where things stop, and terminal velocity is no different. This is where the velocity will stop accelerating - it has reached it's terminal. This is why we call it terminal velocity.
• Question 9

When falling out of a plane, you will initially accelerate at 9.8 m/s2. The average person has a mass of 60 kg. Calculate the force that earth is applying to that person in order to get them to accelerate at 9.8 m/s2

588
EDDIE SAYS
Again, if you know the equation - this is what the answer should look like: F = ma F = ? m = 60 kg a = 9.8 m/s2 F = 60 x 9.8 F = 588N
• Question 10

In your own words, explain what Newtons Third Law is. (2 marks)

EDDIE SAYS
You should now have a bit of an understanding of what Newtons Third Law is (we hope!) but when it comes to explaining it - don\'t be a hero! Just write the equation, it is all the explaining it needs. Don\'t try and remember the quotes from Newton, you never will (let\'s be honest, they are boring!) So just write out the equation and if you can remember the other stuff, that\'s a bonus!