CHS Physics

Making waves

2009-04-07T17:00:00.000-07:00

Hello all. Since I left our unit sound waves hanging I've scoured the web and found a site that will help you make the next step on your own. After break I will be back for one class and one class only (well maybe more) just to let you listen to my lap top make more beeping sounds and possibly to play with slinkies. In the mean time I want you to go to this site http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l3c.html (it's a tutorial on wave interference...which is what happens when you have multiple waves interacting with each other -- check out the links for previous lectures if you find yourself in need of a review). Read through the lecture and aswer the questions. Be sure to try answering them yourself before you click the to see the answer and be sure you really understand the answer that is given once you do check. I would like each of you to email me a short paragraph explaining constructive and destructive interference. If you want you can draw a picture and email me a photo of it (in addition to a written photograph). For extra credit draw a four frame animation of a square wave coming from the right and triangular wave coming from the left. Your frames should cover the time before the two waves intersect, the duration of their intersection and the time after. I will post what I think the first frame should look like soon. All of this is due the monday after spring break. You should look at the site and attempt the questions, however, by the end of this week. I expect to recieve an email from all of you by friday reporting your progress.

Physics Test- due 2/16

2009-02-10T12:45:00.000-08:00

Finally, its here! If you have any questions...Ask!

Gravitaion notes and solutions

2009-02-09T20:02:00.001-08:00

Click on the pages for a larger version. Hopefully the image quality is not too terrible. The test will be up and posted any moment now.

Class/ Home Work January 19

2009-01-19T04:17:00.000-08:00

In the packet on gravity I handed out last week:

1) Review Example Problem 1 (on page 174), also review the work we did together last Monday to calculate the length of the martian year. Do Practice Problems 2 and 4 (also on page 174).

2) On Wednesday we used Newton's Law of universal gravitation to determine the exact value of the constant in Kepler's third law. (This same calculation is performed on page 176 of your packet). You can take this calculation a few steps further to get a formula for determining the period of a planet orbiting the sun. This formula is derived and listed on page 176 of you packet. Use it to do problem problem 6 in the 7.1 Section Review on page 178.

See you Wednesday.

Soulutuons to problems assigned 1/10

2009-01-13T14:56:00.000-08:00

Problems from handout:
17. a) Towards center of circle
b) Towards center of circle
c) Static friction

61.
a) Since the car is moving in a circle you now the acceleration must be a_c=v²/r. You have been given the radius (r=50m) of the circle but you have to find the velocity. The car's lap time is 14.3s and since the track goes around the circumference of a circle the distance the car travels each lap is 2π(r). The velocity (distance/time) is then 2π(50m)/14.3s=22m/s.Now just plug in: a_c=(22m/s)²/50m = 9.68 m/s²b) If you know the acceleration then finding the force is just a matter of multiplying the mass: F_c=ma_c (or F_c=mv²/r).
67. If the pilot is moving at the right speed the only force that will be acting on him at the top of the loop will be gravity -- because that's the only force needed to maintain his motion. The pilot will feel this as a sensation of weightlessness. In this special situation centripetal acceleration is exact provided by gravitational acceleration so that g=v²/r (remember g=9.8m/s²). This problem tells you the pilot's speed and asks you to find the radius:

g=v²/r rearrange and you get: r=v²/g= (120m/s)²/(9.8m/s²)=141.2.

Thats it!