Momentum What is Momentum Momentum Mass in motion

Momentum

What is Momentum? § § Momentum: Mass in motion Non-moving objects have no momentum at all.

How do we calculate momentum § Momentum= Mass x Velocity § § p=mxv Unit: kg x m/s

Which has more momentum? § A Baseball thrown by a major league pitcher at 90 mph § A dump truck moving at 35 mph

Momentum is a vector quantity § The direction of momentum is the same as the direction of velocity Positive momentum Negative momentum

Momentum § Changing the mass changes the momentum

Momentum is changed by force §

Impulse (two definitions) Impulse = Force x time Impulse = Change in momentum Impulse = F t Impulse = m∆v F t = m∆v § Impulse is J, so J = F t = m∆v § Unit = N∙s or kg m/s

Which would you rather hit? Both will stop you, so the change in momentum (impulse) is the same

Does this mean the same force? § No!! Impulse is the same, not force § Fhaystack is less than Fwall § thaystack is greather than twall § The same impulse means the product of the force and time are the same

Impact time is the key § If the impact time is long, the impact force will be small § Impact time = the time during which your momentum is brought to zero. § Impact force = the force that brings you to rest

Examples § What are some examples of things that increase impact time and therefore decrease force? § Airbags § Padded dashboard v. rigid dashboard § Bending your knees when you jump from an elevated position § Relaxing your body when you fall to spread force of impact over more muscles § Falling on a soft mat vs. hard floor § Moving away from or with a punch § EX. Increasing the time of impact 100 times reduces force of impact 100 times. § force and impact time are indirectly proportional. (Two variables that affect impulse)