# Week Thirteen – Investigating Spring Forces & Circular Motion

In Class Activity Plan

90 min – Investigating Spring Forces (Word, Pdf)

PURPOSE: Investigate situation that can’t be modeled with constant acceleration, introduce Hooke’s Law; introduce relationship between forces and energy.

Video Example: (Predictions)

Technical Notes:

• The force sensors need to have their direction reversed so that both the motion sensor and the force sensor see the same direction as positive
• We probably want each group to have a different spring
• They’re going to be coming back to energy at the end of this lab using the force versus displacement graph and the energy stored in the spring

Seed:

• Consider the situation of a person just constantly stretching the spring

o   Draw pie charts for this situation
o   Where does the energy from the person go?

10 min – Whiteboard Investigating Spring Forces
PURPOSE: Summarize results of investigation

Video Examples: (Boarding 1, Boarding 2)

1. What did you learn?
2. What rules can you make?
3. What questions do you still have?

45 min – Whiteboard Discussion

PURPOSE: Investigate situation that can’t be modeled with constant acceleration, introduce Hooke’s Law; introduce relationship between forces and energy.

Video Example: (Discussion)

Goals:

• Hooke’s Law

o o   The slope of the F vs d graph is the spring constant

• Energy stored in the spring

o   Consider the units of the area under the F vs d curve (get to energy stored in the spring)

o   Need to point out this is negative (and makes sense b/c the integral is negative) 20 min – Whiteboard – Spring problems (2): Compression Spring (Word, Pdf) & Crates from a spring (Word, Pdf)

PURPOSE: Practice modeling situations using Hooke’s law, integrating non constant acceleration situations into existing models.

Note: Do one in class and assign the other for homework

25 min – Board Meeting

PURPOSE: Build consensus around modeling situations using Hooke’s law, integrating non- constant acceleration situations into existing models.

Video Examples: (Boarding 3, Boarding 4, Boarding 5)

40 min – Instructor led discussion – Thinking about circular motion

PURPOSE: Introducing circular motion, special type of constant a modeling.

Video Example: (Four perspectives)

Using bowling balls and rubber mallets:

• Ask the students, how would you have to hit the ball in order to get it to move in a circle? Try it.
• Should find that they need to hit the balls toward the center of the circle (or perpendicular to the motion or something similar).
• Confirm with video from Rutgers: Visit website
• Have the students make a motion map for the ball
• Divide the class in quarters, and have each of them find the direction of the acceleration for each ¼ of the motion map on their whiteboard

o   They already know about impulse, so it might be useful for them to be thinking about the force that is changing the momentum in this case

30 min – Whiteboard Discussion

PURPOSE: Use motion maps to determine uniform circular motion as a special case of a constant acceleration model.

• Looking at each sections acceleration and force diagrams, what can we say about the direction of the acceleration? The net force?
• Either show the geometric derivation of the centripetal acceleration or give the handout to get to o   Handout: Centripetal Acceleration Derivation (Word, Pdf)