Misconceptions About Falling Objects

Now I want you to make a prediction: in my left hand I have a standard size basketball, and in my right hand a 5 kg medicine ball. If I drop them both at exactly the same time, which one will hit the ground first?

Ah, this is a trick one, isn't it? The heavy will go down first.

Well, yeah, it'll drop faster. They'll both hit the ground at the same time. Give me a PR. Actually, I would have thought this one would go faster, 'cause it's heavier.

Heavier? Maybe it's that one.

Maybe this one? Yeah, so you reckon that this one will be faster?

So why does that make it faster?

H: 'Cause the weight pulls it down quicker.

What are we measuring when we say, "Oh, it's heavier?"

Gravity.

Gravity, go ahead.

Yeah, oh, objects being pulled to the earth, I guess.

Okay, so which of these objects is being more pulled to the Earth?

This one.

That one? The black one?

All right, well here's what we're going to do. I want you to hold both of those above your head, get really high. Can you? On the count three. Ready?

3, 2, 1...

Yeah, exactly the same. They fell at the same time. Exactly the same time they hit.

It the same time was that what you expected to see?

No.

So what do you make of that?

I need to go read more books. Magic.

Gravity is going to pull it at the same rate no matter how heavy or how light it is.

But gravity is how light or how heavy something is?

One, be massive. There must be some force that's dragging down, and actually, the actual weight of it doesn't mean it doesn’t matter.

Something to do with mass or something? I can't remember. Why?

It's almost like the weight holds it back in a way, even though that doesn't seem to make sense.

I think you might be hitting on an interesting point there. Weight holds it back.

Now it's not actually weight that holds it back, but inertia. That's the tendency of matter to maintain its state of motion. So to remain at rest if stationary, or to continue with constant velocity when in motion.

What's the big idea?

The big idea is this: one has more mass, so it's got more weight, which you can clearly feel, but it's also got more inertia, which means it's also more sluggish, right? It tends to resist acceleration.

So that greater force is required to accelerate it at the same rate as this ball.

Like a heavy car trying to accelerate?

Like a heavy car trying to accelerate, you need more force to get it going.

Exactly. So what does all that mean?

Well, the force on the medicine ball is greater than the force on the basketball, but it has more inertia.

And what's really important is that the ratio of force to inertia is the same for all objects, so everything accelerates at the same rate and lands at the same time.

And the plastic block because it's conducting the heat to the ice cube now. Point.

Growing up, most of us have been captivated by one of these: a slinky.

So why doesn't the space station come crashing into the Earth?