Hooke's Law

Today in physics we reviewed what we did on Friday which was total energy and how the amount of kinetic energy and the amount of potential energy are always equal to the starting total energy.

We then moved on to look a springs, more specifically, Hooke's Law which contains stuff about the spring constant and how far from equilibrium the sping is depressed or stretched.

Ex: A compressed spring that obeys Hooke's law has a potential energy of 18 J. If the spring constant is 400 N/m, find the distance by which the spring is compressed.

Ep = 18 J

k = 400N/m

x = ?

Ep=1/2kx^2

=to find x we manipulate the formula to get the root of 2ep/k

= the root of 36/400

=3/10 or .30m the spring compressed.

We also looked at finding the total energy and the maximum height of an object, in this case, a golf ball.

Ex: Determind the total mechanical enerygy of a 48g golf ball if it has a velocity of 25 m/s when it leaves the club face.

m = .048 kg

vi = 25 m/s

hi = 0 m

et = 1/2mv^2

=1/2(.048)(25^2)

=15J

b) If the golf ball goes in an arc and has a speed of 15 m/s at its maximum height, what will the maximum height be?

h = ?

Et = 15 J

m = .048 kg

v = 15m/s

Et=mgh+1/2mv^2

15J=(.048kg)(9.8m/s^2)(h)+1/2(.048)(15^2)

And to find h we manipulate the formula and eventually get that the height is 20m.

Landon is next.

Roller Coasters!

You will be completing an assignment that uses the Physics of Energy to explain how a roller coaster works.

For Monday I need you to look over the following list of possible websites to use or to select a video that shows a roller coaster in action.  Choose a video or a program to use.
https://docs.google.com/document/d/1Q6nmNhSqJ6Nn-JXg7HFrjm7m_Gdja076XPdRKqFSu3U/edit

If you are using an online game/animation for your roller coaster, on Monday you will be given time on the laptop in the Physics Lab to make a video of your roller coaster in action.

On Tuesday we will go to the computer lab for you to view your video and come up with the explanation that you will present to the class.

On Wednesday, we will present them!

The general idea behind the assignment is:

Create a roller coaster. Use Smart Recorder to record it or save it if you can.

Present your video to the class. Pause the video as you go to explain the physics behind the motion:

Draw on the screen with the SMARTBoard

• key ideas:
• height
• velocity
• kinetic energy
• gravitational potential energy
• gravity
• use given or arbitrary values for the height to explain why the roller coaster works

Potential Energy and the Law of Conservation of Energy

Today in a heated and somewhat violent Physics class, we learned about potential energy and the law of conservation of energy. We started off by finishing the questions on kinetic energy we did the day before on page 290 #1-4

Then we read pages 291 and 292 in the textbook and answered questions about it.

From the reading we learned some new definitions:

Potential Energy- Energy that is stored and capable of being transformed into other types of energy.

Law of Conservation of Energy- Energy is not created or destroyed in any interaction, but is merely transformed from one type of energy into another.

Mr.Banow used the textbook as per usual to show us that when he holds the book above the floor and the book is not moving it has potential energy.

After the reading we moved on to learn about the most common type of potential energy and the one we will use most often in Physics 30 and that is Gravitational Potential Energy.

Gravitational Potential Energy- the energy stored as a result of the vertical position (height) of an object.

The formula to calculate Gravitational Potential Energy is Eg=mgh where:

Eg is Gravitational potential energy (J)

m is mass

g is acceleration due to gravity

h is change in height relative to the reference point

Ex.1

A 25.0kg box is lifted from the floor to a ridiculously large desk that is a whopping 1.87m above the floor.

a) What is the gravitational potential energy relative to the floor?

m=25kg

h=1.87m

g=9.8m/s^2

Eg=?

Eg=mgh

=(25kg)(9.8m/s^2)(1.87m)

=458J

Jeren (soon to be four eyes) Tuchscherererererererererererer is next