work is done and energy is transferred whenever a force moves
Equation For Work Done: Work Done(J) = Force (N) x Distance moved in direction of force (m)
EXAMPLE: A person lifts a 60n parcel by 1.5m. work done is 60N x 1.5m = 90J
A smaller force is needed to drag something up a ramp compared with lifting it directly up. the force along the ramp is working over a long distance, and also needs to work against friction.
Remember! the force must move in order to do work. A person lifting a box does work but when he is just standing with the box he is doing no work because he is not moving.
Gravitational Potential Energy!
Gravitational energy is energy an object has due to its position.The object gains more energy when it is lifted higher above the ground
Equation: Gravitational Potential Energy (joules) = mass (Kg) x Gravity (10N/Kg) x Height (m)
EXAMPLE: The gravitational potential energy gained by a 3kg rabbit lifted 0.8m by its owner is; 3 x 10 x 0.8 = 24J
Investigating Kinetic Energy!
All moving objects have kinetic energy, Kinetic energy is calculated using:
- Kinetic energy (J) = 1/2 x mass (kg) x velocity(squared) (M/S)
- EXAMPLE: Kinetic energy of a person (mass 100Kg) running at 3 m/s is 1/2 x 100 x 3(squared) -450J
The Kinetic energy of an object:
- doubles if mass doubles
- quadruples if the speed doubles
At its highest point, a pendelum has a gravitational energy and no kinetic energy, as it swings down some gravitational energy changes to kinetic energy and back again!