Transcript 4*3 Spring Potential Energy

4*3 Spring Potential Energy
 WDYS? (p372)
1. .
2. .
3. .

WDYT?
Today, a roller coaster gets up to its highest point
by _________ and/or __________.
2. It (does/does not) cost more to lift the roller
coaster if it is full of people.
1.
4*3 Investigate (p373)
 You will detemine the Kinetic Energy (KE) of
the pop-up toy when it leaves the table.
1.
A hop height is ___m, the mass is ___kg
2. GPE = mgh
GPE = KE
KE = ½ (m×v2)
4*3 Investigate (p373)
Position
At rest, on table;
h = 0m
Just after popping;
h = 0m
½ the way up;
h = 0.15m
At peak;
h = 0.3m
SPE (J)
KE (J)
GPE (J)
SPE + KE + GPE =
Conservation of
Energy
4*3 Investigate (p373)
 Energy Bar Chart 
Physics Talk:
Conservation of Energy (374)
Spring Potential Energy
k
x
SPE = ½ (k . x . x )
is the spring constant; units are N/m
is the amount of stretch (compression); units are meters
k = (2 × SPE)
(x . x)
x = √(2 × SPE)
k
Physics Talk:
Conservation of Energy (374)
 Spring Potential Energy (SPE)  energy stored
in a spring due to its compression or stretch
EXAMPLE
bungee cords, trampolines
 The type of energy may change (GPE, KE, SPE)
but the SUM OF THE ENERGY’s must always
be the same!!!
***In some systems, energy can be lost as
thermal energy, sound, and/or light***
Physics Talk:
Conservation of Energy (374)
 But there are sooooo many more types of energies:
electrical, light, nuclear, sound, heat, thermal, chemical
 All energies are measured in JOULES
 If you take into account all forms of energy, the total
number of joules should remain the same
 Law of Conservation of Energy  total energy is
conserved and can be shown in ENERGY BAR CHARTS
Physics Talk:
Conservation of Energy (374)
 ENERGY BAR CHARTS
Physics Talk:
Conservation of Energy (376)
 What is the effect of MASS on energy?
1. _____
2. _____
 Where does the roller coaster get all the GPE
that drives the ride?!?!?!?!?!?!
1. _____
2. _____
3. _____
Physics Talk:
Conservation of Energy (374)

What is the effect of MASS on energy?
1. The lighter and heavier toys have the same SPE
2. They also have the same GPE (because they
cancel each other out)
Where does the roller coaster get all the GPE that
drives the ride?!?!?!?!?!?!
1. Electrical energy (power plant/generator) pulls cart
up the 1st hill
2. After 1st hill, GPE  KE
3. At the end when braking, KE  TE

4*3 TOTD
1.
All energies are measured in _____.
2. In some systems, energy can be lost as __________,
_____, and/or _____.
3. The Law of Conservation of Energy states that
energy is ___________.
4. __________ energy (power plant/generator) pulls
cart up the 1st hill.
5. When does GPE = KE???
Checking Up (p377)
1. The SPE of a pop-up toy gets converted
FIRST to _____ after it leaps off the table,
eventually changing to _____.
2. The pop-up toy will have ____J of KE just
after leaving the table.
3. The toy will have _____J of GPE at the peak
of its rise.
4. The two factors responsible for the amount
of SPE stored in a spring are ____ and ____.
PTG (p380)
Position above
table (m)
SPE (J)
At rest = 0m
25
Just after
popping = 0m
½ up the
height = 0.3m
At peak =
0.6m
KE (J)
GPE (J)
SPE + KE + GPE =
Conservation of Energy
PTG (p380)
2. Make an energy bar chart from Question 1
4. Think of a roller coaster hill…
5. The 2nd hill CANNOT be higher than the 1st because
_____. The total mechanical energy of the ride
CANNOT INCREASE once it is rolling on its own.
6. In real life, the roller coaster is constantly losing energy
due to _____ with the track and is lost as heat.
PTG (p380)
7. Electrical Energy = GPE = _____
8. a) KE = ½ (m × v2) = _____
b) If KE = 0, then GPE = _____
c) h = GPE /(m×g) = _____
9. While the ball is rising, its GPE is _____.
10._____ gain the greatest GPE from start to finish.
PTG (p380)
11. a) GPE = _____
b) SPE = _____
c) h = GPE = _____
(m×g)
KE = _____
12. GPE = SPE
mgh = ½ (kx2)
a) k = 2mgh = _____
x2
b) x = √(2mgh) = _____
k
13. SPE = KE
SPE = ½ (kx2)= _____
4*3 TOTD #2
 A roller coaster car has a mass of 500kg and a
speed of 20m/s…
What is the KE at the bottom of the hill?
2. What is the GPE at the top of the hill?
3. What is the height of the 1st hill?
4. If the brakes fail, then what will the spring constant
(k) be when compressed by 8m? (Look at #12a)
1.
5. If a pop-up toy has a spring constant of 60N/m and
is compressed 0.7m, then what is its SPE?