Download Linking Asteroids and Meteorites through Reflectance

Introduction to Physical Science
Monday, Wednesday, Thursday
Tom Burbine
[email protected]
Quiz #1
Momentum
• Momentum is inertia in motion
• Momentum = mass x velocity
• Momentum = mv
• When you don’t care about direction:
• Momentum = mass x speed
Scalars and Vectors
Momentum
• Moving object can have large momentum if it has
a large mass, large velocity, or both
Momentum
• To change momentum, you need to change the
velocity or the mass of the object
Momentum
• To change the velocity of an object, you need to
apply a force, which accelerates an object
Momentum
• The longer the force is applied,
• The greater the velocity changes,
• The greater the momentum changes
Impulse
• Impulse = Force x time interval
• Impulse = Ft
Questions:
• Compare the momentum of a 1 kg cart moving at 10 m/s
with that of a 2 kg cart moving at 5 m/s.
• Does the moving cart have impulse?
• Does a moving cart have momentum?
• For the same force, which cannon imparts a greater impulse
to a cannonball – a long cannon or a short one?
Answers:
• Compare the momentum of a 1 kg cart moving at 10 m/s
with that of a 2 kg cart moving at 5 m/s.
• Same momentum
• Does the moving cart have impulse?
• No. Impulse is something the cart experiences
• Does a moving cart have momentum?
• Yes
• For the same force, which cannon imparts a greater impulse
to a cannonball – a long cannon or a short one?
• Long cannon. Force acts over a longer time
Impulse and Momentum
• Impulse = change in momentum
• Ft = ∆(mv)
Increase Momentum
• Increase the momentum of an object as much as
possible, apply the greatest force as long as
possible
• For example, a golfer and a baseball player will
swing as hard as possible and follow through
• Following through extends the time of contact
Exercise
Decrease Momentum
• Why is it better to hit a haystack with a runaway
car or a concrete wall to stop?
• You need the same impulse to stop the car
Answer:
• Why is it better to hit a haystack with a runaway
car or a concrete wall if you want to stop?
• You need the same impulse to stop the car
• By hitting the haystack instead of the wall, you
extend the time during which your momentum is
brought to zero
Decrease Momentum
• Break bricks by a large impulse over a short time
• http://www.youtube.com/watch?v=xwAu0KXTuj
Law of conservation of momentum
• In the absence of an external force, the
momentum of a system remains unchanged
• http://www.youtube.com/watch?v=UwWVEpjAI
Dg&feature=related
Net Momentum
• Net momentum (before collision) = Net momentum (after collision)
Types of collisions
• Elastic collision – all the momentum is transferred
to another object during a collision
• Inelastic collision – Colliding objects become
entangled
Recoil Velocity of a gun
• The recoil velocity caused by a gun exactly
balances the forward momentum of the projectile
• http://www.youtube.com/watch?v=X8imjiuOx1c
Exercise
Question:
• If a freight car travelling at 10 m/s hits a car at
rest hits another freight car with the same mass
and the frieght cars become stuck together, what
will be the velocity of the stuck cars?
Answer:
• If a freight car travelling at 10 m/s hits a car at
rest hits another freight car with the same mass
and the frieght cars become stuck together, what
will be the velocity of the stuck cars?
• (net mv) (before) = (net mv) (after)
• (m x 10 m/s) = (2m x v)
• v = 5 m/s
• http://dev.physicslab.org/Document.aspx?doctype
=5&filename=Compilations_NextTime_Moment
um.xml
Homework
• http://www.youtube.com/watch?v=DI3rPT_9rW0
• http://www.youtube.com/watch?v=DYMTAZrKL
cM
Any Questions?