# What is the impulse of friction?

• Jason03
In summary, the conversation involves solving a basic momentum/impulse problem using a graph. The equation used is mv_{1} + P-T(\Delta{t}) = mv_{2}. The area under the curve is used to find the impulse of the applied force, but incorporating the force of friction and its impulse can lead to incorrect answers. The key is to subtract out the kinetic friction, which is considered constant over time.

#### Jason03

I was working on a basic momentum/impulse problem where a block is pushed by a force P over a time T that is plotted on a graph...Kinetic Friction is given but how would I incorporate that into the equation to find the velocity?

I know the impulse is the area under the curve...

$$mv_{1} + F_{avg}\Delta{t} = mv_{}$$

What is the force of friction?
What is the impulse of friction?
How does that change your equation?

Actually I figured it out, pretty easy...I just over thought it as usual...
This equation allowed me to come up with the correct answer

$$mv_{1} + P-T(\Delta{t}) = mv_{2}$$

Im having trouble coming up with velocity for Time at 8 seconds...I came up with the Velocity at 5 seconds easily using the equation above...

heres the graph for the problem...http://img91.imageshack.us/img91/6935/graphmp3.jpg [Broken]

im trying to find the average Force at T = 8 seconds...but its not working

Last edited by a moderator:
Show what you did. To find the impulse of the applied force, find the area under the curve. What about the impulse of the friction force?

I used this equation to solve for time at 5 seconds...and it worked...

$$mv_{1} + P-T(\Delta{t}) = mv_{2}$$

but I tried solving for time at 8 seconds... finding the area under the curve which is just a rectange and triangle...but the answer comes up incorrect

as far as area it should just be $$(L * W) + (.5*b*h)$$

Last edited:
Jason03 said:
I used this equation to solve for time at 5 seconds...and it worked...

$$mv_{1} + P-T(\Delta{t}) = mv_{2}$$
That equation is not quite right. That second term (P) is a force, not an impulse. (It should be the area under that curve.)

but I tried solving for time at 8 seconds... finding the area under the curve which is just a rectange and triangle...but the answer comes up incorrect

as far as area it should just be $$(L * W) + (.5*b*h)$$
Looks fine to me. Show me the details. What did you get for the impulse due to the force P? The impulse due to the friction force T?

Don't forget that Impulse is NET force * time. So if you have the graph of the force of the engine vs. time, you need to subtract out kinetic friction, which is considered constant over the time.

If the MR2 that kept up well with the viper was a Spyder, that is I think 137 hp and not 115 hp.

## What is the impulse of friction?

The impulse of friction refers to the total change in momentum of an object caused by frictional forces acting on it. It is a vector quantity and is measured in units of Newton-seconds (N-s).

## How is the impulse of friction calculated?

The impulse of friction can be calculated using the formula J = Ff x t, where J is the impulse, Ff is the frictional force, and t is the time interval over which the force is applied.

## What factors affect the impulse of friction?

The impulse of friction is affected by several factors, including the coefficient of friction, the surface area of contact, the speed of the object, and the type of surface materials.

## Why is the impulse of friction important?

The impulse of friction plays a crucial role in various real-world scenarios such as braking in cars, slowing down of moving objects, and the movement of glaciers. It helps in understanding the dynamics of objects in motion and is essential in engineering and design applications.

## Can the impulse of friction be negative?

Yes, the impulse of friction can be negative if the direction of the frictional force is opposite to the direction of motion of the object. This indicates that the object is gaining momentum and its speed is increasing.

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