1. Homework Questions

2. Unit 3: Energy and Momentum
Energy Objectives:
1. Define work and calculate the work done by a force.
2. Calculate the kinetic energy of a moving object.
3. Determine the gravitational potential energy of a system.
4. Calculate the power of a system.
5. Apply conservation of energy to analyze energy transitions and transformations in a system.
6. Analyze the relationship between work done on or by a system, and the energy gained or lost by that system.
7. Use Hooke's Law to determine the elastic force on an object.
Calculate a system's elastic potential energy.

3. Elastic Force and Elastic Potential Energy

4. Elastic Force (Hooke’s Law)
Where:
Fs = Spring Force
K = spring constant (N/m)
X = Elongation or change in position from equilibrium (either compression/extension)

5. Resistance Bands and spring constants
Resistance bands are used for resistance training.
These bands allow us to get a 'workout' them because stretching the bands requires AND expends energy.
Resistance bands are available in different tensions (spring constants) and are color coded accordingly.

6. Hooke's Law Fspring = ­kx F (N) x (m)
If we graph the relationship between force and elongation the mathematical relationship can be experimentally confirmed.
Force (effort required to stretch)
x (m)
Displacement (elongation)

7. Varying the displacement/elongation (x)
Hooke's Law
Fspring = ­kx
Varying the displacement/elongation (x)
F (N)
F (N)
x (m)
x (m)
small elongations require small forces
large elongations require large forces

8. Slope of an Force-position graph
Fspring = ­kx
F (N)
Question:
What physical property of the spring do we find if we take the slope of the graph (Rise/Run)?
Force (effort required to stretch)
x (m)
Displacement (elongation)

9. Hooke's Law Rise/Run = F/x = k
Varying the spring constant k (the stiffness of the spring) The spring constant is related to the slope the line.
F (N)
Spring Constant = slope of line (Newtons/meter)
x (m)

12. Hooke's Law Fspring = ­kx
Varying the spring constant k (the stiffness of the spring) The spring constant is related to the slope the line.
F (N)
large spring constant
small spring constant
x (m)

13. Elastic Potential Energy
The energy imparted to a spring by the work done must be stored in the Elastic Potential Energy (EPE) of the spring:
Like all forms of energy, it is measured in Joules (J).

14. Note 1
For some reason, the regents exam loves to focus on two types of questions for the regents (Reading a spring constant off of a graph and Two-step problems), so your packet focuses on those two types of questions – However, that doesn’t mean that all problems are two-step.

19. Note 2: Vertical mass on a spring
When talking about masses hanging vertically from a spring, the weight is balanced by the spring force, so they are equal in magnitude and can be used to solve spring problems.

22. Practice Time/Exams back/Labs