PHYS 1750: SELECTED TOPICS in PHYSICS
LECTURE 10. Work and Energy.
6.i. | Concept of Energy | ||
6.1. | Work as a Form of Energy | ||
1. | Concept of path of motion | ||
2. | Work when force is constant | ||
a. |
W = F . d =
Fdcosq :
note W is a scalar Fcosq is the component of force parallel to the path | ||
b. | Units: Newton*meters = Joules | ||
c. | Don't confuse with torque, which has the same units | ||
6.2. | Kinetic Energy | ||
1. | Definition: Ek=mv2/2; also Joules | ||
2. | Work-K.Energy theorem: change in K.E. = work. | ||
3. |
Derivation in cases of parallel, constant force: W=Fd=mad, use 2ad=v2-vo2, then W=mv2/2 - mvo2/2 | ||
6.3. | Gravitational Potential Energy | ||
1. | What happens when work is done against gravity? | ||
2. | Definition: Ep=mgh | ||
6.4. | Spring Potential Energy | ||
1. | What happens when work is done against a spring? | ||
2. | Hooke's Law: F = kx | ||
a. | x = displacement from equilibrium | ||
b. | k = spring constant | ||
3. | Force not constant: use average force: Ep=W=Fd=(kx/2)x=kx2/2 |
Review Questions follow next lecture.
Lecture 11: Conservation of Energy