Momentum
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- Pages: 32
Momentum • Sports Analogy • Physics definition vs sports definition • Name the actress for a Raffle Ticket
Momentum • Momentum = mass x velocity or p = mv • Units = kg – m/s
Momentum is a vector.
Momentum • p = mv • Human Head = 4.0 Kg • Name the movie for a raffle ticket
Momentum • HITT- What is the momentum of a human head traveling East at 6.0 m/s? • A) 6.0 kg-m/s East B) 12 kg-m/s West C) 24 kg-m/s East D) 24 kg-m/s West
Momentum • How can you get an object to change its momentum? • Change its mass or change its velocity. • Remember – a change of velocity can occur by changing the speed (meters per second) AND/OR changing the direction
Momentum • HITT
Q - And how can you get an object to change its velocity?
A)Apply a Force in the direction of the motion B) Apply a Force in the opposite direction of the motion C) Apply a Force perpendicular to the motion D) all the choices are correct This is Newton’s Second Law of Motion said in a different form
Momentum • • • • •
F=m a F = m (∆v/∆t) F ∆t = m ∆v Impulse = F ∆t units are Newton-Sec Change in Momentum = m ∆v units are kg-m/s
Momentum • m ∆v = F ∆t • Change in Momentum = Impulse • The impulse is always equal to the change in momentum as long as there are no external forces = closed system.
Momentum • HITT- A Force of 12 N West acts on a 4.0 kg ball for 3.0 s. The ball is at rest. • What is the magnitude of the impulse? A) 12 N-s B) 36 N-s C) 48 N-s • What is the change in momentum? A) 12 N-s B) 36 N-s C) 48 N-s • What is the change in velocity? A) 4 m/s East B) 4 m/s West C) 9 m/s East D) 9 m/s West
Momentum • HITT – A 2.0 kg Soccer ball has an initial velocity of 5.0 m/s down and rebounds up at 5.0 m/s up.
• HITT- a) In what direction is the impulse? • A) Up B) Down b) In what direction is the change in momentum? • A) Up B) Down c) What is the change in the velocity? A) 0 m/s B) 5 m/s C) 10 m/s
Momentum
Momentum • An egg (0.1 kg) is flying through the air at 20. M/s.
• How are we going to stop it?
Momentum • An impulse! A large force in a short time is the same impulse as a small force for a long time. How shall we catch it? • Demo
Momentum • Examples with cars– air bags, seat belts, sand bags, trees, telephone poles….
Momentum
• http://www.regentsprep.org/Regents/physics/phys01/acc
Take a look at this web site to watch an old car crash!!!!
Momentum
• http://www.regentsprep.org/Regents/physics/phys01/acc htm
Notice the difference with crumple zones!!
Momentum • The Battering Ram – useful for entering castles. Your choice – the battering ram is to be made of clay or a superball?
Momentum • Try this web site to prove that momentum is always conserved as long as there are no external forces. • http://www.mhhe .com/physsci/physical/ jones /elastic_collisions/ ΣF = 0
• HITT- What is ∆v if the battering ram slows down from 12 m/s east to 10 m/s east as it smashes through the castle door? • A) 2 m/s East B) 2 m/s West C) 22 m/s East D) 22 m/s West
Momentum
• HITT- What is ∆v if the battering ram rebounds off the castle door from 12 m/s east to 10 m/s West? Notice that this is a rebound and therefore a greater ∆v • A) 2 m/s East B) 2 m/s West C) 22 m/s East D) 22 m/s West
Momentum
Newton’s 3rd Law • For every action there is an equal an opposite reaction. • Forces come in pairs! • I push you – You push me. Q - I walk forward by having the floor push with 200 N against my foot. What is the reaction to this action?
Newton’s 3rd Law
• Q – I weigh 700 N because the Earth attracts me. What is the reaction for this action?
Newton’s 3rd Law • Notice the pairs. • Notice that the action always acts on one body while the reaction always acts on the other body. • -Describe each action-reaction pair.
Newton’s 3rd Law
• http://archive.ncsa.uiuc.edu/Cyberia/VideoTestbed/Proje
• Find the action – reaction pair.
• DEB• Action = __________ • Reaction = _________
Momentum • • • • •
Demos 1 - rocket on wire 2 – jumping 3 – fan and lab cart 4 – projectile launcher
Conservation of Momentum • Momentum is always conserved unless there is an external force. • If there is an external force, that means there is an impulse and that means there is a change in momentum.
Conservation of Momentum
• m1v1 + m2v2 = m1v1` + m2v2` if the event is elastic • m1v1 + m2v2 = (m1 + m2 ) v` if the event is inelastic
Conservation of Momentum
• Special case for inelastic if the target (m2 ) is at rest. • m1v1 = (m1 + m2 ) v`
Momentum • Demos– • 1 – skateboards in the hall Center of mass • 2 – Air track • 3 – Newton’s Cradle • 4 – Egg and basketball • 5 – Ballistic Pendulum • 6 – Spin in chair – angular momentum
The Discrepant Event • 3 vs 1 Collision
Momentum • Momentum = mass x velocity or p = mv • Units = kg – m/s
Momentum is a vector.
Momentum • p = mv • Human Head = 4.0 Kg • Name the movie for a raffle ticket
Momentum • HITT- What is the momentum of a human head traveling East at 6.0 m/s? • A) 6.0 kg-m/s East B) 12 kg-m/s West C) 24 kg-m/s East D) 24 kg-m/s West
Momentum • How can you get an object to change its momentum? • Change its mass or change its velocity. • Remember – a change of velocity can occur by changing the speed (meters per second) AND/OR changing the direction
Momentum • HITT
Q - And how can you get an object to change its velocity?
A)Apply a Force in the direction of the motion B) Apply a Force in the opposite direction of the motion C) Apply a Force perpendicular to the motion D) all the choices are correct This is Newton’s Second Law of Motion said in a different form
Momentum • • • • •
F=m a F = m (∆v/∆t) F ∆t = m ∆v Impulse = F ∆t units are Newton-Sec Change in Momentum = m ∆v units are kg-m/s
Momentum • m ∆v = F ∆t • Change in Momentum = Impulse • The impulse is always equal to the change in momentum as long as there are no external forces = closed system.
Momentum • HITT- A Force of 12 N West acts on a 4.0 kg ball for 3.0 s. The ball is at rest. • What is the magnitude of the impulse? A) 12 N-s B) 36 N-s C) 48 N-s • What is the change in momentum? A) 12 N-s B) 36 N-s C) 48 N-s • What is the change in velocity? A) 4 m/s East B) 4 m/s West C) 9 m/s East D) 9 m/s West
Momentum • HITT – A 2.0 kg Soccer ball has an initial velocity of 5.0 m/s down and rebounds up at 5.0 m/s up.
• HITT- a) In what direction is the impulse? • A) Up B) Down b) In what direction is the change in momentum? • A) Up B) Down c) What is the change in the velocity? A) 0 m/s B) 5 m/s C) 10 m/s
Momentum
Momentum • An egg (0.1 kg) is flying through the air at 20. M/s.
• How are we going to stop it?
Momentum • An impulse! A large force in a short time is the same impulse as a small force for a long time. How shall we catch it? • Demo
Momentum • Examples with cars– air bags, seat belts, sand bags, trees, telephone poles….
Momentum
• http://www.regentsprep.org/Regents/physics/phys01/acc
Take a look at this web site to watch an old car crash!!!!
Momentum
• http://www.regentsprep.org/Regents/physics/phys01/acc htm
Notice the difference with crumple zones!!
Momentum • The Battering Ram – useful for entering castles. Your choice – the battering ram is to be made of clay or a superball?
Momentum • Try this web site to prove that momentum is always conserved as long as there are no external forces. • http://www.mhhe .com/physsci/physical/ jones /elastic_collisions/ ΣF = 0
• HITT- What is ∆v if the battering ram slows down from 12 m/s east to 10 m/s east as it smashes through the castle door? • A) 2 m/s East B) 2 m/s West C) 22 m/s East D) 22 m/s West
Momentum
• HITT- What is ∆v if the battering ram rebounds off the castle door from 12 m/s east to 10 m/s West? Notice that this is a rebound and therefore a greater ∆v • A) 2 m/s East B) 2 m/s West C) 22 m/s East D) 22 m/s West
Momentum
Newton’s 3rd Law • For every action there is an equal an opposite reaction. • Forces come in pairs! • I push you – You push me. Q - I walk forward by having the floor push with 200 N against my foot. What is the reaction to this action?
Newton’s 3rd Law
• Q – I weigh 700 N because the Earth attracts me. What is the reaction for this action?
Newton’s 3rd Law • Notice the pairs. • Notice that the action always acts on one body while the reaction always acts on the other body. • -Describe each action-reaction pair.
Newton’s 3rd Law
• http://archive.ncsa.uiuc.edu/Cyberia/VideoTestbed/Proje
• Find the action – reaction pair.
• DEB• Action = __________ • Reaction = _________
Momentum • • • • •
Demos 1 - rocket on wire 2 – jumping 3 – fan and lab cart 4 – projectile launcher
Conservation of Momentum • Momentum is always conserved unless there is an external force. • If there is an external force, that means there is an impulse and that means there is a change in momentum.
Conservation of Momentum
• m1v1 + m2v2 = m1v1` + m2v2` if the event is elastic • m1v1 + m2v2 = (m1 + m2 ) v` if the event is inelastic
Conservation of Momentum
• Special case for inelastic if the target (m2 ) is at rest. • m1v1 = (m1 + m2 ) v`
Momentum • Demos– • 1 – skateboards in the hall Center of mass • 2 – Air track • 3 – Newton’s Cradle • 4 – Egg and basketball • 5 – Ballistic Pendulum • 6 – Spin in chair – angular momentum
The Discrepant Event • 3 vs 1 Collision
