# If you roll when you hit the ground you feel less velocity?

Rolls or brake falls slow down how fast your body hits the ground by well rolling.How does this decrease impacted.

Mentor
It is not so much the rolling itself, it is making the deceleration last longer, which means you get a lower peak acceleration. As you can't compress yourself to a point, you have to go sidewards.

Staff Emeritus
Gold Member
As an old saying goes: "It's not the fall that kills you, it's the sudden stop at the end." Rolling lessens the "suddenness" of the stop.

Thoams Jerome
Does anyone have the equation for that?

It is not so much the rolling itself, it is making the deceleration last longer, which means you get a lower peak acceleration. As you can't compress yourself to a point, you have to go sidewards.
How does not being able to comprising yourself to a point, effect you going sidewards?Also if you dropped a object like a box with lightly connected object to hollow space.Like putting a rock that's lighter then the box in the top connected with toilet paper.then dropping it down would the rock go up and take some the energy from the fall with it?

Staff Emeritus
2022 Award
Also if you dropped a object like a box with lightly connected object to hollow space.Like putting a rock that's lighter then the box in the top connected with toilet paper.then dropping it down would the rock go up and take some the energy from the fall with it?

I'm sorry but I can't make any sense out of this.

berkeman
Mentor
I'm sorry but I can't make any sense out of this.
I think he's asking about jumping up in a falling elevator to lessen the impact at the bottom (maybe), but I'm not getting the toilet paper angle...

I think he's asking about jumping up in a falling elevator to lessen the impact at the bottom (maybe), but I'm not getting the toilet paper angle...
Sorry.If you drop a trash can with a light board lightly wedged inside.Will the board jump up when the trash can hits the ground?What are the physics involved.

pixel
Does anyone have the equation for that?

In a fall, you are changing momentum from some initial value to a zero final value. The change in momentum equals the Impulse, which is the integral of the force (in this case the force causing the deceleration) over time. If you can increase the time over which the force acts, less force on average is required. If you don't use a brake or roll fall, the time interval is much smaller so the force is larger to produce the same momentum change.

If you don't know calculus, instead of the integral of force over time just think in terms of the product of the average force and the time interval over which the force acts.

Staff Emeritus
2022 Award
Sorry.If you drop a trash can with a light board lightly wedged inside.Will the board jump up when the trash can hits the ground?What are the physics involved.

The board will likely become un-wedged and fall to the bottom of the trashcan upon impact. During the impact, the board experiences a large force from friction that attempts to decelerate it. If, before the board decelerates, it slides enough to break loose completely then it will fall to the bottom.

Mentor
How does not being able to comprising yourself to a point, effect you going sidewards?
It doesn't, and no one said that.
It is advisable to go sidewards. Bending your knees is an example already, and starting to roll is an extension of that approach.

Kaura
Does anyone have the equation for that?

F = ΔP/Δt

Force known in this case as Impulse is equal to a body's change in momentum divided by the change in time. Momentum is the object's mass multiplied by its velocity. From this equation you can see that the longer it takes for the momentum to reach zero the less force acts on a body. In the example of rolling when hitting the ground, doing such a thing gives the person's body more time to change its momentum to reach rest. It is also why landing on a cushion from a high height is far less likely to hurt you compared to landing on concrete. The cushion allows for your body to slow down over a longer period of time.