Work Done against….
In many situations gravitational potential energy is converted into kinetic energy, or vice versa. Some everyday examples of this are:
Swings and pendulums If we pull a pendulum back we give it GPE, when it is released it falls, losing its GPE but speeding up and gaining KE. When it passes the lowest point of the swing it begins to rise (gaining GPE) and slow down (losing KE).
Bouncing or throwing a ball Holding a ball in the air gives it GPE, when we release this it transforms this into KE. As it rises it loses KE and gains GPE.
Slides and ramps A ball at the top of a slide will have GPE. When it reaches the bottom of the slide it has lost all its GPE, but gained KE.
In each of these cases it appears as though we have lost energy. The pendulum doesn’t swing back to its original height and the ball never bounces to the height it was released from. This is because work is being done against resistive forces.
The swing has to overcome air resistance whilst moving and the friction from the top support.
The ball transforms some energy into sound and overcoming the air resistance.
Travelling down a slide transforms energy into heat due to friction and air resistance
The total energy before a transformation = The total energy after a transformation
| Section 4 | Hooke’s Law | |
|---|---|---|
| Lesson 11 | ||
| Learning Outcomes | To be able to state Hooke’s Law and explain what the spring constant is | |
| To be able to describe how springs behave in series and parallel | ||
| To be able to derive the energy stored in a stretched material | M.BENYOHAI |