linear momentum ap physics chapter 7. linear momentum 7.1 momentum and its relation to force

Linear Momentum

AP Physics

Chapter 7

Linear Momentum

7.1 Momentum and Its Relation to Force

7.1 Momentum and Its Relation to Force

Linear momentum – product of an objects mass and its velocity

Unit is a kgm/s

The quantity is only useful when discussing collisions

7-1

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7.1 Momentum and Its Relation to Force

Impulse

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7.1 Momentum and Its Relation to Force

Impulse

7-1

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7.1 Momentum and Its Relation to Force

Impulse

Or

7-1

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7.1 Momentum and Its Relation to Force

In a collision, to decrease force, we increase time of the collision

Air Bags

7-1

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Linear Momentum

7.2 Conservation of Momentum

7.2 Conservation of Momentum

Two kinds of collisions

1. Perfectly elastic – objects bounce apart

2. Perfectly inelastic – objects stick together

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7.2 Conservation of Momentum

In reality collisions are a combination of the two.

Law of Conservation of Momentum – in a closed system, momentum is conserved in a collision

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0p p

7.2 Conservation of Momentum

In an elastic collision

Direction of velocity is given by the sign of the velocity.

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0 0A A B A A A B Bm v m v m v m v

7.2 Conservation of Momentum

In an inelastic collision

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0 0( )A A B A A Bm v m v m m v

7.2 Conservation of Momentum

In an explosion

The reverse of a

Inelastic collision

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Linear Momentum

7.3 Conservation of Momentum in Collisions

7.3 Conservation of Energy and Momentum

Energy (mechanical) is conserved in an elastic collision

So

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0 0A A B A A A B Bm v m v m v m v

0 0

2 2 2 21 1 1 12 2 2 2A A B B A A B Bm v mv v m v m v

7.3 Conservation of Energy and Momentum

Any collision in which energy is lost, is considered inelastic.

7-3

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7.4 Collisions in Two Dimensions

7.4 Collisions in Two Dimensions

inelastic collisions in two dimension

As always each dimension is treated independently

Then use vector addition to calculate the final answer

7-4

0 0( )A A x B A x A B xm v m v m m v

0 0( )A A y B A y A B ym v m v m m v

x yv v v

Linear Momentum

7.5 Center if Mass

7.5 Center of Mass

Even if an object rotates there is one point that moves in the same that a particle would move if subject to the same force.

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7.5 Center of Mass

Center of mass – the point that does not rotate

Center of gravity – the point at which the force of gravity can be considered to act

7-5

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