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Impulse

Impulse is a quantity that describes the effect of a net force acting on an object (a kind of "moving force").

It is represented by the symbol J.

It is the product of the average net force acting on an object and its duration.

J = F*Δt

It is the force–time integral (a concept requiring knowledge of calculus).

It is a vector quantity (since force is a vector and time is a scalar).

Real life applications of impulse

If Mike Tyson throws a punch at Silly and Silly is too silly to dodge it, what do you think he should do?

a. Go against the punch

b. Not do anything and take the punch

c. Go with the punch

When you are playing golf, why do you do follow through?

Do you do follow through in other sports?

How do airbags in your car protect you from serious injuries?

Lets consider a collision between two cars, red and blue.

When they collide, they exert equal and opposite force on each other. So we can say that F (red)=F (blue)

What can we say about the time for which they are interacting with each other? Do you think it could be different for red than for blue?

So what can you say about the impulse that red car experiences compared to that of blue car?

Formula and units

p=mv

, where p is momentum, m is mass and v is velocity.

Definition

Momentum is defined as 'mass in motion' or 'Inertia in motion'.

**Momentum and Impulse**

Collisions:

Momentum is a commonly used term in sports. A team that has the momentum is on the move and is going to take some effort to stop.

Momentum is a physics term; it refers to the quantity of motion that an object has.

Momentum

**By Divya Sharma**

Units of momentum could be derived by using the formula.

Momentum is a vector quantity.

A net force is required to change an object's momentum.

Momentum is directly proportional to mass and velocity.

Something heavy and slow could have the same momentum as something light and fast.

is a quantity that describes an object's resistance to stopping (a kind of "moving inertia").

Practice problems:

Determine the momentum of a ...

a. 60-kg halfback moving eastward at 9 m/s.

b. 1000-kg car moving northward at 20 m/s.

c. 40-kg freshman moving southward at 2 m/s.

A car possesses 20 000 units of momentum. What would be the car's new momentum if ...

a. its velocity was doubled.

b. its velocity was tripled.

c. its mass was doubled (by adding more passengers and a greater load)

d. both its velocity was doubled and its mass was doubled.

Impulse-Momentum Theorem

The impulse-momentum theorem states that the change in momentum of an object equals the impulse applied to it.

J = Δp

If mass is constant, then…

FΔt = mΔv or Ft = mΔv

Units of impulse

:

The SI unit of impulse is the newton second.

A 0.50-kg cart (#1) is pulled with a 1.0-N force for 1 second; another 0.50 kg cart (#2) is pulled with a 2.0 N-force for 0.50 seconds.

Which cart (#1 or #2) has the greatest acceleration?

Which cart (#1 or #2) has greater impulse?

Which cart (#1 or #2) has the greatest change in momentum?

Cart #2 has the greatest acceleration. Recall that acceleration depends on force and mass. They each have the same mass, yet cart #2 has the greater force.

The impulse is the same for each cart. Impulse is force*time and can be calculated to be 1.0 N*s for each cart.

The momentum change is the same for each cart. Momentum change equals the impulse; if each cart has the same impulse, then it would follow that they have the same momentum change.

When you apply an unbalanced force on an object, it accelerates the object and hence changes its velocity which changes the momentum of the object.

We also know from Newton's first law that F=ma.

How can you prove Ft= p or Ft = mΔv?

Definition:

A collision is an interaction between two objects that have made contact (usually) with each other. As in any interaction, a collision results in a force being applied to the two colliding objects.

You will learn that there are two types of collisions,

Elastic collisions

and

Inelastic collisions.

In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces often cause one object to speed up (gain momentum) and the other object to slow down (lose momentum).

Conservation of momentum:

Conservation of momentum is one of the most powerful laws in physics.

The total momentum of an

isolated system

should stay constant.

An isolated system is a system that is free from the influence of a net external force.

For example: An object in equilibrium.

Elastic and Inelastic collisions:

Elastic collisions are collisions in which the total momentum and kinetic energy of the system stays constant.

Ex: When we worked on the lab on Newton's third law.

Inelastic collisions are collisions in which the total momentum of the system stays constant but kinetic energy doesn't.

Most all of the real life collisions are inelastic.

In either of the cases the total momentum of the system should stay constant as long as the system is isolated.

End of presentation.