 # Circular and Projectile Motion

In this worksheet, students will explore the definition and principles of circular and projectile motion. Key stage:  KS 4

Curriculum topic:  Physics: Forces and Motion

Curriculum subtopic:  Acceleration Caused by Forces

Difficulty level:   ### QUESTION 1 of 10

When I was a child at the beach, I used to spin a bucket of water around and around my head. So long as I kept the bucket spinning that water would stay in the bucket and I wouldn't get wet. But then my older brother would come along and stop the bucket from spinning and soak me... Annoyed, I was always wondering why it took just a little bit of time for the water to realise that it had stopped spinning and fall on my head. This activity will give you all of the information that 8-year-old and very wet me was wondering as I plotted my revenge against my brother.

Circular motion:

For an object to move in a circle, a force has to act on it all the time. It is called centripetal force and it acts towards the centre of the circle. Gravity is the centripetal force that keeps planets moving around the Sun and satellites moving around planets. Gravity is the force that attracts masses in the universe; it depends on the masses involved and decreases as the distance between the objects decreases. It follows an inverse square law and can be shown by this equation: It means that the force between two objects is inversely proportional to the distance between them squared, so if the distance is doubled, the force between the objects decreases to one quarter.

Projectile motion:

A ball is a projectile, because it moves through the Earth's gravitational field. It follows a parabolic trajectory (called parabola), which means it falls towards the ground because of the Earth's gravity. Other projectiles are javelins and darts. Once a projectile moves, the only forces acting on it are gravity and air resistance. The latter is usually ignored.

You must remember two things about projectile motion:

1.      The horizontal velocity remains constant

2.      The vertical velocity increases as gravity accelerates the projectile

Two factors affect the range of a projectile:

1.      Its initial velocity

2.      Its launch angle

The faster it travels at the start, the larger the range.

When does a force act on an object that follows a circular motion?

At the end

All the time

At the beginning

What is the name of the force that acts on an object when it moves in a circular manner?

Centrifugal force

Centripetal force

Centriole force

What is the universal force between masses?

Momentum

Thrust

Gravity

What is the effect on the centripetal force when the distance between the objects decreases?

Decreases

Increases

Stays the same

Which law does the centripetal force follow?

Parabola law

Proportionality law

Inverse square law

How will the centripetal force be affected if the distance between the two objects triples?

x 9

÷ 3

÷ 9 What type of motion is shown in the picture?

Square

Cylindrical

Circular

Select two examples of projectile objects.

Parachute

Darts

Cannonball

Aeroplane

What is the name of a projectile’s motion?

Parabola

Tombola

Parasola

Which velocity remains constant in a projectile trajectory?

Vertical

Horizontal

Neither

• Question 1

When does a force act on an object that follows a circular motion?

All the time
EDDIE SAYS
A force acts on an object that follows a circular motion all the time. If they stop, then the water falls out. I'm not bitter or anything...
• Question 2

What is the name of the force that acts on an object when it moves in a circular manner?

Centripetal force
EDDIE SAYS
The force that acts on an object when it moves in a circular manner is called centripetal. Interestingly - there is no such thing as centrafugal force. We only use it to describe an effect that happens.
• Question 3

What is the universal force between masses?

Gravity
EDDIE SAYS
Gravity is the centripetal force that keeps planets moving around the Sun and satellites moving around planets. Gravity is the force that attracts masses in the universe, it depends on the masses involved and decreases as the distance between the objects decreases.
• Question 4

What is the effect on the centripetal force when the distance between the objects decreases?

Increases
EDDIE SAYS
The centripetal force INCREASES when the distance between the objects decreases. Think about when you spin things - it is harder to keep them gonig when they are close to you.
• Question 5

Which law does the centripetal force follow?

Inverse square law
EDDIE SAYS
The centripetal force follows the inverse square law.
• Question 6

How will the centripetal force be affected if the distance between the two objects triples?

÷ 9
EDDIE SAYS
The centripetal force will become one ninth of what it was, if the distance between the two objects triples.
• Question 7 What type of motion is shown in the picture?

Circular
EDDIE SAYS
The image displays a circular motion. You can see the objects are moving in a circle, so circular motion.
• Question 8

Select two examples of projectile objects.

Darts
Cannonball
EDDIE SAYS
Two projectiles are cannonball and darts, as the dart is projected forward by a human's hand, and a cannon ball is projected from a cannon and, thus, move through the earth's gravitational field.
• Question 9

What is the name of a projectile’s motion?

Parabola
EDDIE SAYS
A projectile’s motion is called parabola. This is the name of an interesting shape - why not google it and take a look.
• Question 10

Which velocity remains constant in a projectile trajectory?

Horizontal
EDDIE SAYS
The horizontal velocity remains constant in a projectile trajectory. This is true when the object is thrown only.
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