Chap.9: Forces and Energy

Question 1

Define friction

Answer 1

It is the force that opposes motion between two surfaces in contact

Question 2

What is elastic force

Answer 2

Force acting on a stretched or compressed elastic object to return it to its original shape

Question 3

Difference between mass and weight

Answer 3

Mass: Amount of matter in an object, remains constant
Weight: Gravitational force exerted on an object, changes with location

Question 4

What does transfer of energy between objects cause?

The 4 ways

Answer 4

1. Changes in the state of rest or motion of an object
2. Changes due to the turning effect of an force on an object
3. Changes of shape or size of an object
4. Changes of pressure on an object

Question 5

Define pressure

Answer 5

Force exerted per unit area in contact

Question 6

What is the formula for pressure

Answer 6

Force/Area
In N/m2 or Pa

Question 7

Define work done

Answer 7

The application of a force on an object that causes it to move in the direction of the force

Question 8

Conditions for work to be done on an object

Answer 8

• Force is applied to it
• Object moves
• It moves in the same direction as the force

Question 9

Formula of work done

Answer 9

Work done (J)= Force (N) x distance (m)

Question 10

What is the Principle of Conservation of energy?

Answer 10

• Energy cannot be created nor destroyed
• Energy can be transfered from one store to another
• Total energy of an isolated system is constant

Question 11

Formula of Kinetic store

Answer 11

1/2 (m)(v)2

Question 12

Formula of Gravitational potential store

Answer 12

gps= mgh