Conservation of Energy
Total mechanical energy stays constant when no work is done on or by the system
Name the energy changes in this video.
School blocks YouTube? BlobLaunch.mov
Try This at Home!
School blocks YouTube? Onsite
St. Mary's U. Astronomy and Physics Dept.
Video Instruction
D) Law of Conservation of Energy
Unless work is done on or by a system, its total mechanical energy does not change.
Was energy created in this video?
Girl goes flying after the biggest piggy-back blob jump
School blocks YouTube? BlobLaunch.mov
The massive PE of the men on the platform completely turned into KE at the bottom of their jump.
The boy on the blob has more KE but less PE than the men.
1. Total Mechanical Energy
Ex 1) Falling object (no friction)
Answer
Predict how far up the incline each ball will go.
(assume no friction)
Why does each ball rise to the same height from which it began?
PE depends only on height.
Ball stops when all KE turns into PE.
Energy changes in a roller coaster
— Teachers Domain
Ex 2) Roller coaster track
If KE at A = 0 → PE = ?
PE = mgh (use g = 10 m/s2)
PE = 3 kg × (10 m/s2) × 3 m
| PE | KE | |
|---|---|---|
| A | 90 J | 0 |
Point B
m = 3 kg, h = 1 m
| PE | KE | |
|---|---|---|
| B | 30 J | 60 J |
Point C
m = 3 kg, h = 0
| PE | KE | |
|---|---|---|
| C | 0 J (h = 0) | 90 J |
Point D
m = 3 kg, h = 1 m
| PE | KE | |
|---|---|---|
| D | 30 J | 60 J |
Point E
m = 3 kg, h = 0
| PE | KE | |
|---|---|---|
| E | 0 J (h = 0) | 90 J |
Point F
m = 3 kg, h = 1 m
| PE | KE | |
|---|---|---|
| F | 30 J | 60 J |
Point G
m = 3 kg, h = 3 m
| PE | KE | |
|---|---|---|
| G | 90 J | 0 J |
Point H?
Physics of Designing Rollercoasters
At what minimum height should you place the ball so it makes it all the way around the loop?
UC Irvine
School blocks YouTube? LoopTheLoop.mov | LoopTheLoop.mpg
The ball has to be placed at a height above the top of the loop so it has the KE to continue.
