Forces between objects

Question 1

What is a force?

Answer 1

A force is a push or pull that is caused by interacting with something.

Question 2

What are the two types of force?

Answer 2

All forces are either contact or non-contact forces.

Question 3

When is a force a contact force?

Answer 3

When two objects have to be touching for a force to act, the force is called a contact force.

Question 4

Examples of contact forces

Answer 4

Friction, air resistance, tension in ropes, normal contact force, etc.

Question 5

When is a force a non-contact force?

Answer 5

If the objects do not need to be touching for the force to act, the force is a non-contact force.

Question 6

Examples of non-contact force

Answer 6

Magnetic force, gravitational force, electrostatic force, etc.

Question 7

What does Newton’s third law of motion state?

Answer 7

Newton’s third law of motion states that when two objects interact with each other, they exert equal + opposite forces on each other.

Question 8

What is the unit of force?

Answer 8

The unit of force is the newton abbrieviates as n.

Question 9

Examples of Newton’s third law of motion

Answer 9

→ A boxer who punches a bag with a force of 100N experiences an equal + opposite force of 100N from the bag.
→ The weight of an object is the force of gravity on an object due to the Earth. The object exert equal + opposite forces on the Earth.
→ Two-roller skaters pull on opposite end of a rope. The skaters move towards each other because they pull on each other with equal + opposite forces(Two newton-metres could be used to show this).
→ The Sun + Earth are attracted to each other by the gravitational force. This is a non-contact force. An equal but opposite force of attraction is felt by both the Sun and the Earth.

Question 10

How to get a car stuck in mud out of the mud?

Answer 10

• A car stuck in mud can be difficult to move.
• A tractor can be useful here.
• At any stage, the force of the rope on the car is equal to the force of the car on the rope.
• To pull the car out of the mud, the force of the mud on the tractor need to be greater than the force of the mud on the car.
• These two forces are not equal + opposite to each other.
• The ‘equal and opposite force’ to the force of the mud on the tractor is the force of the tractor on the mud.
• The ‘equal an opposite force’ to the force of the mud on the car is the force of the car on the mud.

Question 11

What is the driving force?

Answer 11

The driving force on a car is the force that makes it move.

Question 12

What else can the driving force be know as?

Answer 12

This is sometimes called the engine force or the motive force.

Question 13

What does the driving force do?

Answer 13

• The force pushes the car forward because there is no friction between the ground and the tyre of each drive wheel.
• Friction acts where the tyre is in contact with the ground.

Question 14

What happens when the car moves forward?

Answer 14

When the car moves forward:
* The force of the friction of the road on the tyre is in the forward direction.
* The force of the friction of the tyre on the road is in the reverse direction.
→ The two forces are equal + opposite to each other.