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Monday, November 19, 2007

Physics Month Continues



We’ve been having a BLAST (sometimes literally) this month exploring force and motion. So far, we’ve explored Newton’s three laws of motion by doing some fun experiments. Are you a bit rusty on ol’ Newton? Here’s a breakdown and some of the hands-on activities we’ve used:

NEWTON’S FIRST LAW OF MOTION:
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

We tested this law by the “lazy coin” activity. We put a playing card over an empty jar. Then we placed a coin on top of the card and gave the card a quick flick. The card flew off the jar and landed on the table – the coin, however, dropped into the jar. Why? Because the coin is heavier, it has more inertia than the paper does and is harder to move.

NEWTON’S SECOND LAW OF MOTION:
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

In other words:

If an object is at rest, it is considered to have zero speed. So any force that causes that object to move is an unbalanced force. Any force (such as friction or gravity) that causes an object to slow down or speed up is an unbalanced force.

By building (and playing with) our own hovercrafts, we saw the very real effects of friction and resistance. We also made parachutes of varying sizes and dropped eggs from a high spot. In this last case, we used the entire scientific method – from asking the question, forming a hypothesis, testing and recording. The photograph above shows Megan and Sara before a big launch.

NEWTON’S THIRD LAW OF MOTION:
For every action, there is an equal and opposite reaction.

Newton’s third law was demonstrated by blasting a balloon across a string and making pinwheel rockets.

1 comment:

Daniel said...

Physics: Best left to the professionals?

Calvin and I were talking about Newton's laws. Unfortunately, I mixed up Newton's second and 'fourth' laws and got a blank stare...realizing my mistake, I spent some time explaining Newton's 'fourth' law of planetary motion--which turns out to really be Kepler's second law. Go figure. Anyhow...

We discussed how hard we'd have to push to move a car very slowly and how fast a soccer ball would go with the same push [force].

I then puzzled him with this question: In space, where everything is weightless (we imagined being in a big space gym), is it harder to push a car or a soccer ball? Why? [Newton's Second Law: Even though it's "weightless," it still has a mass and F=ma.] If we pushed really, really hard and moved the car, what would happen? [Newton's First Law: It keeps going.] Would it hurt if it hit somebody? How hard would someone have to push to stop it? [Newton's Third Law: Exactly as hard as we pushed to get it moving.]

So far, so good. But I felt compelled to continue...if I could just work Newton's 'fourth' law into the discussion:

If we spent a month in space during Northern-hemisphere summer and then a month in winter, when Earth is traveling faster around the Sun, how do the areas of the 'pie pieces' swept out during each month compare? [Newton's 'fourth' law = Kepler's second law: They're the same...]

Oh well. Maybe I should just leave this to the professional!