Springs

simple harmonic motion

 

1. Work-Energy principle proof.

2. Springs

  • Hooke's Law: F = -kx. k is the spring constant.
  • Maximum velocity and zero velocity
  • Maximum acceleration and zero acceleration

3. Potential Energy of Springs.

Work done in compressing an extended spring. W = 1/2kx2

Examples: Toy gun, ball falling to a spring, bungee jump. Giancoli pg 164

HW. PG 113: 7, 8, 12, 26, 27, 34, 35

 

 

 

POWER

 

1. Conservation of Energy. Total energy cannot be created or destroyed but can only be transformed from one form into another.

If mechanical energy is lost it goes into another form like heat or sound so that the total energy is conserved.

2. Power. The quantity of work performed within a time interval.

Power = (change in Work)/(change in time)

The unit is J/s or W (watts). Also commonly put in terms of horsepower. 1 hp = 746 W.

Power = Fv ... can you prove this?

Q16.

3. Efficiency is the ratio of useful energy to the total energy transferred.

Efficiency = (useful power OUT)/(total power IN)

Q18

4. Kinetic Energy and Momentum

Totally elastic = momentum and KE are conserved

Totally inelastic = when the bodies stick together after collision and KE is lost (thermal, deformation, sound).

Links 1 , 2

PG 113: 14-18, 20, 22, 23, 24, 25, 26, 27, 34, 35.