00:01
Okay, so we've got you're jumping in the air.
00:03
You've got five different explanations.
00:04
We want to see which of these is the best and then explain why that one is the best.
00:09
So let's go through all five of them and eliminate the wrong ones and then i can explain the right one.
00:14
So for a, upward force by the ground pushes you up, but this force cannot exceed your weight.
00:20
So if you think about the force is acting on you when you jump, you start from rest, right? you've got the force of gravity or your weight on you.
00:27
In order to accelerate, the normal force has to be bigger than the force of gravity.
00:32
So a is going to be no good for that.
00:34
The force has to exceed your weight in order for you to jump.
00:38
Choice b, you're able to spring up because the earth exerts an upward force on you.
00:43
No, the earth exerts a downward force on you.
00:45
That's gravity.
00:46
So that one's wrong.
00:47
C, since the ground is stationary, it cannot exert an upward force on you.
00:51
It can.
00:51
It has to.
00:52
That's the only way that you're going to accelerate upward.
00:55
D, you push down on the earth with a greater force than your weight.
00:58
The earth pushes you back with the same magnitude, propels you into the air.
01:02
So this is going to be the correct answer.
01:03
We can explain it in just a second here.
01:05
And then lastly, when you jump, the earth exerts a force on you and you exert a different force on the earth.
01:10
By newton's third law, this one can't be correct.
01:13
The force that you exert on the earth should be equal to the force that the earth exerts on you.
01:17
So why is the correct? so i think we actually need two diagrams for this to really explain it properly...