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Home Minds On Momentum, Collisions and Explosions Mission MC3 Impulse and Momentum Change Variables Help Help 4

Mission MC3 Impulse and Momentum Change Variables

The Question

A moderate force will break an egg. If an egg is dropped on the hard floor, it usually breaks. Yet if it is dropped on soft ground, it will often 'survive' the impact without breaking. A collision with soft ground protects the egg by increasing the ____ and decreasing the ____.

Physics Rules

Momentum Change - Impulse Theorem:
When a force is exerted upon an object in a collision, the object is said to have encountered an impulse. The impulse is simply the mathematical product of the force exerted on the object and the amount of time over which it was exerted. The impulse changes the object's momentum and is equal to the amount of momentum change.
 
Impulse = Momentum Change
or

F•t = m•∆v

Minds On Time

If an egg strikes the ground with 1 unit of momentum and comes to a stop, then there will be a momentum change of 1 unit. This momentum change is achieved through an impulse of 1 unit (see the Know the Law section). Somehow, sufficient force for a specified amount of time must provide 1 unit of impulse to change the egg's momentum by 1 unit. If the collision occurs with a hard surface, the impulse is 1 unit; if the collision occurs with a soft surface, the impulse is 1 unit. This 1 unit of impulse is based on the pre-collision mass and velocity of the egg; and changing the surface is not going to alter these values.
 
However, changing the surface from a hard floor to soft ground will change the manner in which the 1 unit of impulse is obtained. Impulse is force multiplied by time; and together, the product must be 1 unit. A collision with soft ground will result in the 1 unit of impulse by a larger time and a smaller force (compared to the small time and a large force for the hard floor). The greater give of soft ground extends the time over which the collision lasts and in turn decreases the force that is needed to obtain the required 1 unit of impulse.

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