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Baseball
• Why are baseball players encouraged to “follow through” when hitting the ball with a bat?
Common usage of the term “Momentum”
• A team that has momentum is on the move and is going to take some effort to stop. – “Going into the final weeks, the St. Louis Cardinals
have the momentum." – The headlines declare “Pittsburgh Steelers Gaining
Momentum."
• A team that has a lot of momentum is really on the move and is going to be hard to stop.
• Momentum is a physics term; it refers to the quantity of motion that an object has.
• Refers to how hard something is to stop.
• 1330 Jean Buridan “the true measure of an object’s motion”
• 1600’s Rene Descartes “quantity of motion
• Galileo “Momento”• Newton “Momentum”
Momentum (from latin, meaning movement)
Momentum Defined
p = m vp = momentum
m = mass
v = velocity
Yep…….that’s p for Momentum!!!
Unit must be kg m/s
• So momentum of an object depends on the amount of stuff moving (mass), and the velocity at which the stuff is moving.
• Question? Under what conditions of motion would a semi-truck and a roller skate have the same momentum?
Road Train in the Australian Outback
Equivalent Momenta
Bus: m = 9000 kg; v = 16 m /s p = 1.44 ·105 kg · m /s
Train: m = 3.6 ·104 kg; v = 4 m /s p = 1.44 ·105 kg · m /s
Car: m = 1800 kg; v = 80 m /s p = 1.44 ·105 kg · m /s
Momentum Facts
• Momentum is a vector quantity
• Velocity and momentum vectors point in the same direction
• SI unit is the kg·m/s ( no special name)
• Momentum is a conserved quantity
• Momentum is directly proportional to mass and velocity of object
Momentum Facts
• A net force is needed to change a particular object’s momentum (a change in velocity)
• Something big and slow can have the same momentum of something small and fast
Momentum Examples
10 kg 3 m /s
10 kg30 kg · m /s
p = 45 kg · m /s at 26º N of E
5 g
9 km /s26º
Now, find the vertical and horizontal components of the momentum>>>>>
Sample problems
• Find the magnitude of the momentum of a car of mass 725 kg moving at a velocity of 100. km/h.
Sample problems
• Calculate the velocity of a car that has a mass of 2175 kg and the same momentum as the previous car.
Impulse• In order to change the momentum of an
object, a force must be applied– Gives an alternative statement of
Newton’s second law…..– Watch as a little mathematical magic
is performed!Magic???