Which Hits The Ground First?

Now I'd like you to make a prediction. In my left hand, I have a basketball; in my right hand, a 5 kg medicine ball. If I hold them both above my head and then let them go simultaneously, which one will hit the ground first?

Six years ago here at the University of Sydney, I did an experiment very similar to this where I handed out a heavy object and a light object and I asked which one would hit the ground first. Tell me, which one's going to hit the ground first?

I'm going to put my money on the black ball. What's your heart telling you?

I reckon it's going to drop faster.

I’m on the black one as well.

Yeah, I'll go with you.

Okay, this one will go faster and hit the ground first.

This one? You're going to pick that one?

What's your feeling about that one? How does it compare to the other?

Well, it's a lot heavier, and I just feel like the weight is pulling it down. You know, the more weight, it's the faster it's going to fall to the ground. The forces are more on that ball than this one. You can definitely tell the difference.

I mean, I go to the gym like 7 days a week, but I still feel it. I can still feel it.

Well, that one feels like it could almost go up, while this one, it's got air in it. So, it’s lifting up as opposed to this one being pulled down.

Now, I think... now you're coming back to me. I'm thinking the basketball now.

What's making you think basketball?

'Cause you're coming back to me. I'm just saying, like, no, you know... I’m going to stay so you can't corrupt me. I'm on the black.

Alright, let's actually do this thing. Do you want to hook us up as high as you can? The key is to be as simultaneous as you can.

Alright, are you ready? You want to count it down?

Yeah. 3, 2, 1... oh! 3, 2, 1... yes, we did it!

What did you think happened?

I thought the black one went first.

You thought the black one landed first?

We'd have to go to the tape. Exactly. Wait, what did you see?

They looked like they pretty much landed at the same time.

Same. They hit the ground at the same time.

Oh, I thought it was very close. It was probably just a beat—tick in it.

It’s because it’s not a very high distance, so they haven’t really reached their maximum velocity yet.

Oh, the black ball just didn't reach terminal velocity. There wasn't enough time for it to fall.

I would have thought it would be like all the different variables. Like, um... so that one had to break more air, whatever.

Break more air... you know the answer is: although the force of gravity on the black ball is greater, it has a greater mass and therefore greater inertia. So it requires more force to accelerate it.

There's less gravitational force on the basketball, but because its mass is lower, it has less inertia and therefore requires less force to accelerate it at the same rate as the medicine ball.

Let's give it a try. 3, 2, 1...