Physics 2.3 Work And Energy

Work done

A force does work when it causes an object to be displaced through a distance

Work done equation

Work done = Force x Distance

W = Fd

Work done (Joules), Force (Newtons), Distance (meters)

One joule of work

When a force of one newton causes a displacement of one metre

Work against friction

Energy is transferred to heat causing a rise in temperature due to kinetic energy being converted to thermal energy

Elastic object force and extension

Extension is directly proportional to force applied provided the limit of proportionality is not exceeded

Inelastic deformation

A permanent deformation where the object does not return to its original shape when the force is removed

Plastic deformation

Another term for inelastic deformation

Hooke’s law equation

Force equals spring constant multiplied by extension force in newtons spring constant in newtons per metre extension in metres

Elastic potential energy

Energy stored in a spring when it is stretched or compressed

Compression in springs

Compression can replace extension in the spring force equation

Kinetic energy

The energy stored in a moving object

Gravitational potential energy change

Increases when an object is lifted

Kinetic energy equation

Energy equals one half multiplied by mass multiplied by velocity squared energy in joules mass in kilograms velocity in metres per second

Gravitational potential energy equation

E=mgh

Energy = Mass x Gravitational Field Strength x Height

Energy (J), Mass (kg), Gravitational Field Strength (N/kg), Height (m)

Aerodynamic car shape

More streamlined shapes reduce energy wasted to air resistance

Braking force and stopping distance

If velocity increases the braking force must increase to stop in the same distance

Consequences of large deceleration

Brakes can overheat and the driver may lose control

Seatbelts and safety

Seatbelts increase the time taken to stop reducing the force on the passenger