Energy

Pendulum

Conservation of energy on a swinging pendulum

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Do Now warm-up prompt

Name the energy changes in a windmill.

Wind turbine

Try This at Home!

Insta-freeze

Kent Chemistry Demos

Dissolved gases in a liquid lower the freezing point temperature. When the gases leave, the liquid is able to freeze.

Show Me The Physics

YouTube Channel

Fill in the Blank Notes

Ex 3) Pendulum

Pendulum animation

Where is PE max? KE max? PE = 0? KE = 0? KE = PE?

[ Flash ] — Show Me The Physics

Pendulum energy diagram
Given

If PE at A = 10 J, KE = 0

PEKE
A10 J0 J
B0 J10 J
D10 J0 J
Question

If PE at C = 3 J, KE = ?

Pendulum diagram
↓

KE = 7 J

Ex

If the Wf as the pendulum moves from A to B is 1.5 J, what are the KE and PE of the pendulum at the bottom of the swing?

Pendulum with friction work
↓

PE = 0 J

KE = 8.5 J

Question

Wind turbines convert one form of energy into another. What is that conversion?

Wind turbine
Teachers — check out this clipart archive: Wpclipart
↓

Kinetic energy → electric energy

All Pendulums

PE max. at

Extremes

KE max. at

Bottom

PE at extremes =

KE at bottom

KE @ extreme =

Zero

PE @ bottom always =

Zero

Ex 4

Given

A 1.0 kg pendulum swings to a height of 0.20 m above its lowest point.
What is the KE of the pendulum at the lowest point?

Pendulum PE to KE

PE @ A = KE @ B

PE = mgh
= (1.0 kg)(9.8 m/s2)(0.20 m)

PE = 1.96 J

PE = KE @ B = 2.0 J

Tire swing
Ex

A pendulum is pulled to the side and released. Which plot of d vs PE is correct?

d vs PE plot choices
↓

Answer

Correct d vs PE plot

Review

Pendulum energy review

Ex 5

Given

A 5.00-kg cart is at the foot of a hill 10.0 m high. For the cart to reach the top of the hill, what is the minimum KE of the cart in the position shown?
[neglect friction]

Cart at bottom of hill

m = 5.00 kg

h = 10.0 m

KE = ?

↓

KE at bottom = PE at 10.0 m

KE = PE
= mgh = 5.00 kg × (9.8 m/s2) × 10.0 m

KE = 490. J

Finding the height of a pendulum from a pendulum angle

Pendulum height from angle diagram 1
Pendulum height from angle diagram 2
Pendulum height formula

Enrichment

Owl on a book

Pendulum Top View

[ Flash ]

Foucault's Pendulum — Proved the Earth rotates

School blocks YouTube? Foucault_PendulumReal.wmv

Pendulum mounted on a rotating base

School blocks YouTube? Foucault_Pendulum.mpg | Foucault_Pendulum.wmv

Keeping Accurate Time: a pendulum clock with its escapement and pendulum labeled, a simple pendulum of length L, and the formula T = 2 pi times the square root of L over g NYSSLS Reading Passage icon

NYSSLS Reading Passage · Energy

The Pendulum Through History: How a Simple Swing Changed Science

Open Reading Passage →

Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. Where is a swinging pendulum's kinetic energy greatest?

2. A frictionless pendulum has 10 J of PE and 0 J of KE at its highest point. At a point where PE = 3 J, what is its KE?

3. A pendulum starts with 10 J of PE at the top. If 1.5 J of work is done against friction on the way down, its KE at the bottom is

4. A 1.0 kg pendulum swings to a height of 0.20 m above its lowest point. What is its KE at the lowest point? (g = 9.8 m/s²)

5. What energy conversion takes place in a wind turbine?

Energy Problems →