Monday, May 5, 2008

Introduction to Energy

Feynman block story
Around the class asking for forms of energy (places energy can hide)

Indicated the main forms of energy we will be concerned with: work, gravitational potential energy, kinetic energy, elastic potential energy, heat

Importance of energy is that if you add up all the places energy can hide before something happens and then do it after something happens, you will get the same number. Conservation of energy. The equation is the energy balance equation.

Showed equations for various forms of energy:
GPE = m*g*h = gravitational potential energy = energy of location or position
KE = 1/2 * m * v^2 = energy of motion
elastic PE = 1/2 * k * x^2 = energy stored in a stretched rubber band or spring with spring constant k and stretch x

Went over RA 6.1 on work

Discussed work in detail. Work = F * d where F is the component of force in the direction of motion. If the force is perpendicular to the direction of motion (velocity) no work is done by that force.

Compared work and impulse.

Did example of lifting block showing that work done is equal to the change in gravitational potential energy.

Showed some energy balance equations.

Handed out RA 6.2 due tomorrow.
If students scored less than 85 on the last test, the WebAssign assignment is required and due for tomorrow.