Q:

Please explain the concept of inertia on a model car running down a ramp, and how it may vary by varying the weight of the car in different trials.

- Bill Dismer (age 13)

Vernon Hills, Ill.

- Bill Dismer (age 13)

Vernon Hills, Ill.

A:

Bill -

First, let's think about what inertia is. You can think of inertia as how much something wants to keep doing what it's doing. For example, if you have a book sitting on a table, it's not going to all of a sudden start moving - this is because it wants to keep sitting still: it has inertia. Another example is if something's rolling across the floor - it'll keep going until something stops it. This is inertia, too.

So what makes something have more or less inertia? Well, what makes it easier or harder to change how fast something's moving? Let's say you have a little rock and a great big boulder. The great big boulder is going to be a lot harder to get to start moving, so it has more inertia. And let's say you have a toy car rolling across the ground and a real car on the road. Which is harder to stop? The real car, of course, since it has more inertia - that is, it wants to keep doing what it's doing more. So, if something has more mass it has more inertia.

So you know you can overcome inertia by using a force (like you use a force to move the rock or stop the toy car). And the more inertia it has, the more of a force you need to overcome it and change what it's doing. Ok...on to the car on the ramp. For the car on the ramp, gravity's pulling it down, speeding it up. So gravity overcomes the inertia that wants it to keep going at the same speed.

-Tamara

First, let's think about what inertia is. You can think of inertia as how much something wants to keep doing what it's doing. For example, if you have a book sitting on a table, it's not going to all of a sudden start moving - this is because it wants to keep sitting still: it has inertia. Another example is if something's rolling across the floor - it'll keep going until something stops it. This is inertia, too.

So what makes something have more or less inertia? Well, what makes it easier or harder to change how fast something's moving? Let's say you have a little rock and a great big boulder. The great big boulder is going to be a lot harder to get to start moving, so it has more inertia. And let's say you have a toy car rolling across the ground and a real car on the road. Which is harder to stop? The real car, of course, since it has more inertia - that is, it wants to keep doing what it's doing more. So, if something has more mass it has more inertia.

So you know you can overcome inertia by using a force (like you use a force to move the rock or stop the toy car). And the more inertia it has, the more of a force you need to overcome it and change what it's doing. Ok...on to the car on the ramp. For the car on the ramp, gravity's pulling it down, speeding it up. So gravity overcomes the inertia that wants it to keep going at the same speed.

-Tamara

*(published on 10/22/2007)*