Mr. Light’s Blog

Speed is distance divided by time.  If no time passes, an object doesn’t move any distance.  Doesw that mean that there is no such thing as instantaneous speed?  If not, does the speed disappear every instant and reappear after a millisecond has passed?  What happens to the momentum?

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!

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 . . .

I really enjoyed reading your ideas about “Instantaneous Speed”. As I asked in yesterday’s post, “Is there such a thing as “Instantaneous” speed? If speed is distance divided by time, how can you have speed for an “instant”?”

You had some interesting ideas, but I don’t think we resolved the issue. Here is what some of you said:
Brittany said:

I don’t think it is possible to determine instant speed. It would be near impossible to find a persons EXACT point, and then determine their exact speed. Actually, if you tried to find the speed at an exact point, I don’t think they would even really be moving. But, Mr. Light I don’t really understand what instantaneous speed, if you could please explain it when you get back, I would appreciate it.

Ari said:

I don’t know what instantaneous speed is. I don’t think that it is possible to say what the exact speed of something is in an instant.

Brea said:

The slope tool was a line that you could drag along the line, and it would tell you the speed at that time. I don’t know if there is such a thing as Instantaneous speed. I am not quite sure I understand what it means. Help!!

Zach, Rob, Tyler, and Isaac (Master of all people) said:

There is no such thing as Instntaneous speed because at an instant you do not move.

Kristen said:

Then we used the slope tool to determine the slope of the line at the given point. The slope shows the speed of the walker at the given point.

but she also said:

Another question that you asked is if I think there is such as an instantaneous speed and I am not really sure, but I do know that speed is distance divided by time. Although I am really not sure I don’t think there can be such a thing because the person would have to move in that instant for it to even be posible and it takes time from what you want to do to go from your brain to that part of your body so chances are there isn’t such a thing as instantaneous speed but if there is it would be a really really small decimal.

So what do you think? Let’s define “instantaneous speed” is speed at a particular point in time. Can you be moving during an “instant”. We said that motion is a change in position. Can you change your position in an instant? If you aren’t moving in an instant, do you stop each “instant”? I want to hear what you think.