Mr. Light’s Blog

We’ve experimented with pendulums. Share your ideas about at least one of these questions.

• How does changing the length of the pendulum change its period? Why?
• How does changing the mass of the pendulum change its period? Why
• Some pendulums have two different periods, in 2 different directions. These pendulums move in some pretty interesting ways. How can you make a pendulum with 2 different periods? What will it do when it swings?

Here a few websites that might help you with that last question.
Here’s a picture of one of these pendulums:
http://www.artflowdesigns.com/auction/GIpendulumslate.jpg
Here’s the pattern it can make:
http://static.flickr.com/55/108601845_9bec9951bb_m.jpg http://www.sciencekit.com/category.asp_Q_c_E_436521
Directions for making a 2-period pendulum:
http://www.sfu.ca/physics/outreach/activities/pendulumpictures.htm

Check out this website video Nate found and try to explain it.

http://www.treca.org/staff/voss/Pages/Newtonlaws5.html

Many of you said the heavier car went faster.  How much faster?  If it went faster, it must have accelerated faster.  What was the acceleration of the light, medium, and heavy cart when they were on the same track?

We set some carts rolling down a ramp.  How did your hypotheses turn out?

• What happened to the velocity as it rolled down?
• What happened to the acceleration as it went?
• How did making the ramp steeper change things?
• How did making the cart heavier change things?

We had a fashion show in class yesterday. The most stunning creation was the Newton Hat. This hat was modeled by several members of our class. Tell us about Isaac Newton’s hat!

Vernal Pool by Stone Rd.

I’ve been out walking through the woods a lot this last week. There are a lot of small pools of water out there. Saturday night I went out with my friend Mark and explored a couple of the pools.

Ice on a vernal pool.

We heard hundreds of wood frogs and peepers. The peepers hurt my ears. We saw a lot of wood frogs floating around in the pools. I thought that the wood frogs would have a black mask like the one’s I’ve seen on-line, but these didn’t. The peepers, despite their deafining roar, are harder to see. I did find and photograph several. I even was able to watch some calling, but couldn’t get close enough to photograph these without scaring them into silence.

Wood Frog

Wood Frog eggs.

Spring Peeper

We also saw a lot of spotted salamanders. It is great watching them swim through the water. These are apparantly the “boy” salamanders. The girls will be out later. The salamanders did leave their spermatophores behind. These are gel-covered white containers of sperm that the females will pick up later.

Spotted Salamander

Spotted Salamander in pool.

Spotted Salamander spermatophores.

We had some trouble last week answering the question, can you feel motion? Most people thought that you could. Well, today we did a couple of experiments. Could people always tell whether or not they were moving? What made it so they could tell? When couldn’t they tell? Why? What about those “virtual reality” rides?

So here’s a few questions about moving, velocity, and acceleration.

1. If your eyes are closed and you are moving in a straight line at 10 km/hr, can you tell? How? What if you can’t hear anything and you move very smoothly?
2. How about the same thing, but you are flying in an airliner at 500 km/hr. There is no turbulence. Will this feel different than sitting on the runway? Can you feel the motion now? Explain.
3. You are in a monorail train and it hits the brakes. How can you tell?
4. You are in a space ship moving through the solar system at 10,000 km/hr. What does it feel like?
5. Can you feel motion? Can you feel acceleration? What do they feel like?

Acceleration and Deceleration

Several of you explained this well. Brea said:

1. Well no, all fruit are not apples. If you think of it as a container, it is easier to think about. Acceleration is the big container, and decelleration is a smaller container that can fit inside it. But the big container, acceleration, can’t fit inside deceleration. That relates to the frog question because frog is the small container, and my answer, amphibian, is the big container.

How about the weird units? Acceleration is the change in velocity in a certain time. Velocity, like speed is distance/time so the units must include a distance unit and a time unit. Meters per second, miles per hours, feet per year (glaciers?). Acceleration is change in speed / time so the units need to include a speed unit and a time unit. Since speed already includes a time unit, acceleration ends up with two time units. Meters per second per second, miles per hour per second, etc.

Make up an acceleration problem. Post it. Then, choose someone elses to solve. Explain how you solved it.

Example:

A skydiver is falling at 120 miles/hour. She opens her parachute and slows down to 20 miles/hour in 4 seconds. What was her acceleration?

Good luck!

We have been reading about acceleration. Soon we will be experimenting on it. We ran into some interesting questions.

Why are the units meters/sec/sec or km/hr/sec or km/hr/hr or miles/hr/sec? Could they be feet/year/year??

Why is turning a corner acceleration? How about hittiing the brakes?

Finally, try this: Decelleration is to acceleration as frog is to . . .