# Force and impulse relationship

### What are momentum and impulse? (article) | Khan Academy

This simple relationship means that doubling either the mass or velocity of an object will simply The useful thing about momentum is its relationship to force. Momentum is a measure of how difficult it is to stop something. Impulse is a quantity that describes the effect of a net force acting on an object (a kind of. the impulse of force can be extracted and found to be equal to the change in momentum of an object provided the mass is constant.

The concept of impulse that is both external and internal to a system is also fundamental to understanding conservation of momentum.

Momentum in space Most people are familiar with seeing astronauts working in orbit. They appear to effortlessly push around freely floating objects. Because astronauts and the objects they are working with are both in free-fallthey do not have to contend with the force of gravity. However, heavy moving objects still possess the same momentum that they do on earth, and it can be just as difficult to change this momentum.

Suppose that an emergency occurs on a space station and an astronaut needs to manually move a free-floating 4, kg space capsule away from a docking area. On earth, the astronaut knows she can hold a 50 kg weight above herself for 3 seconds.

### Force, Momentum, and Impulse

How quickly could she get the capsule moving? We first calculate the total impulse that the astronaut can apply. Note that the astronaut is pushing vertically in both cases so we don't need to keep track of the direction of the force. A force acting for a given amount of time will change an object's momentum. Put another way, an unbalanced force always accelerates an object - either speeding it up or slowing it down.

**Force and Momentum**

If the force acts opposite the object's motion, it slows the object down. If a force acts in the same direction as the object's motion, then the force speeds the object up. Either way, a force will change the velocity of an object.

And if the velocity of the object is changed, then the momentum of the object is changed. Impulse These concepts are merely an outgrowth of Newton's second law as discussed in an earlier unit.

### Momentum and Impulse Connection

To truly understand the equation, it is important to understand its meaning in words. In words, it could be said that the force times the time equals the mass times the change in velocity. The physics of collisions are governed by the laws of momentum; and the first law that we discuss in this unit is expressed in the above equation.

The equation is known as the impulse-momentum change equation. The law can be expressed this way: In a collision, an object experiences a force for a specific amount of time that results in a change in momentum. The result of the force acting for the given amount of time is that the object's mass either speeds up or slows down or changes direction. The impulse experienced by the object equals the change in momentum of the object.

In a collision, objects experience an impulse; the impulse causes and is equal to the change in momentum.

## Impulse & Momentum

Consider a football halfback running down the football field and encountering a collision with a defensive back. The collision would change the halfback's speed and thus his momentum. If the motion was represented by a ticker tape diagramit might appear as follows: At approximately the tenth dot on the diagram, the collision occurs and lasts for a certain amount of time; in terms of dots, the collision lasts for a time equivalent to approximately nine dots.

In the halfback-defensive back collision, the halfback experiences a force that lasts for a certain amount of time to change his momentum.