Work Done & Energy Transfer

When is work done (First type)

When an object is moved over a distance by a force applied in the direction of its displacement

It is said that the force does … on the object

work

What does it mean in terms of work when a force is applied but doesn’t result in any movement

No work is done

How is work done when a ball is lifted to a height above the ground?

The weight on the ball produced by the gravitational field does work on the ball over a distance equal to the height of the ball

How is work done when a bird flies through the air?

Air resistance does work against the bird as it flies through the air

What two things is the amount of work done related to?

What formula do we use to calculate work done?

What unit do we use?

• The size of the force and the distance moved by the object in the direction of the force

• Work done = force x distance (W = F x s)

• Joules (J) or newton-metres (Nm)

What is the simple conversion between J and Nm?

What statement can we make from this information then concerning what a joule is equal to?

• 1J = 1Nm

• One Joule is equal to the work done by a force of one newton acting through one metre

What happens whenever any kind of work is done?

Energy is transferred from one store to another

What is mechanical (or electrical) working?

An energy transfer pathway

How is the amount of energy transferred related to the work done (with an equation)

energy transferred (J) = work done (J)

 

What happens if a force acts in the direction that an object is moving to its energy?

It will gain energy (energy is transferred to its kinetic store)

What happens if a force acts in the opposite direction to the movement, to its energy?

It will lose energy (energy is transferred away to the thermal store of the object and the surroundings)

When an object is lifted vertically in the air, how is energy transferred and to which store of the object?

• mechanically

• gravitational potential store

Name the energy the following are related to:

-changes in speed

-changes in height

-changes in shape

• kinetic energy

• gravitational potential energy

• elastic potential energy

What is friction?

A force that works in opposition to the motion of an object

How is energy transferred when friction is present?

What does this do to the object and its surroundings ( and why )?

• by heating (energy is transferred to the thermal store)

• the work done against the frictional forces causes this rise of temperature

What do imperfections at the interface between the object and surface do during friction?

What does this do to the object (2 things) ?

• Bump and rub up against each other

• Slows object down and also causes a transfer of energy to the thermal store of the object and the surroundings

What happens during air resistance and how is energy transferred and why?

• Particles bump into the object as it moves through the air

• As a result, energy is transferred by heating due to the work done against the frictional forces

What happens to a return module of a rocket and why as it travels a distance through the atmosphere?

• heats up

• due to work done by air resisitance