Physics (Impulse)

 

Impulse is a very important equation to understand for optimization of performance. The equation itself is derived from the Force equation (F = MA)

The steps to get the impulse equation are as follows:

F=MA

Step 1: Break down the acceleration formula from the force equation into its velocity pieces.

F= M*(Vf-Vi)/time

 

Step 2: Move the “time” underneath the change in velocity to the force side of the equation via multiplying each side by time.┬áBy multiplying each side by “time”, the “time” on the right side of the equation will be canceled out

F(time)= M*(Vf-Vi)

 

 

When mass is constant (not changing) we can use the equation above, however, if mass is changing you can simply multiply mass by the velocities, so it will look like this below.

F(time) = MVf-MVi

The above formula has some benefits from an analysis perspective. MVf-MVi is a representation of the change in momentum. Momentum = Mass * Velocity.

What can we tell from these formulas?

lets look at F(time) = Mass (Vf-Vi)

This formula tells us that we can use one of two methods for changing momentum (right side of the equation is unchangeable in this example). We can either increase the force expressed on the left or we can increase the time (on the left) that the force is being expressed.

 

Lets look at how this applies in a real life example. Lets an athlete performing depth jumps and he weighs 100kgs and upon landing he is moving at 4m/s. So, our momentum right before ground contact is 100kgs * 4m/s = 400m/s/kg. Now in order to stop this momentum we can use one of two methods…

Force * (Time) = 400m/s/kg

Method one (large force)

800kgs * (0.5 seconds) = 400m/s/kgs

or

Method 2 (larger time)

400kgs * (1 second) = 400 m/s/kgs

 

In both situations thee athlete meets the requirements to stop his momentum. However, the method of accomplishing the task was done in two different ways. The first method used an increase in force and the second relied on an increase in time a lesser force was being applied. Depending on the training goals you may want to emphasize one method over the other.

Impulse and Performance

 

The impulse equation can be used to determine the change in momentum, which means it can tell you how much objects slow down, as well as speed up. We can actually use the momentum equation to determine vertical jump heights, barbell heights, and outcomes of pretty much any movement.

 

Follow Up Video On Impulse

 

 

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