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Momentum and Impulse
N/A
46
Physics
Not Applicable
10/01/2012

Term
 WHEN THINGS COLLIDE
Definition
 When two things collide, the effect they have on each other depends on thier mass and initial velocity
Term
 FORCE AND OBJECTS
Definition
 Sir Isaac Newton realised that a force is needed to change the velocity of an object
Term
 THE EFFECT OF A FORCE
Definition
 Depends on the amount of force and the objects mass
Term
 MOMENTUM DEFINITION
Definition
 Of a moving object; = Mass x Velocity   p = mv
Term
 FORCE NEEDED TO GIVE AN OBJECT A CERTAIN ACCELERATION
Definition
 Force = mass x acceleration   F = ma
Term
 WHERE DOES NEWTONS LAW OF MOTION NOT APPLY?
Definition
 Inside an atom (quantum physics), Speeds approaching the speed of light or in strong gravitational fields (Einstiens theory of relativity)
Term
 MOMENTUM BASICS
Definition
 Unit is kgms-1 Vector quantity - direction is same as the velocity
Term
 NEWTONS FIRST LAW OF MOTION
Definition
 An object remains at rest or in uniform motion unless acted on by a force (so basically a force is needed to change the motion of an object)
Term
 CONSTANT MOMENTUM
Definition
 This means there is no resultant force acting on it  If the mass remains constant and the object has a constant momentum, the velocity will be constant; if the object lost/gained mass whilst moivng, velocity would change to keep momentum constant
Term
 NEWTONS SECOND LAW OF MOTION
Definition
 The rate of change of momentum of an object is proportional to the resultant force on it. The resultant force is proportional to the change of momentum per second
Term
 DERIVING F = ma
Definition
 An object of mass m is acted by a constant force of F. Initial momentum = mu , Final momentum = mv Force is proportional to change of momentum per second. F≈mv-mu/t  F≈ m(v-u)/t a = v-u/t F ≈ ma F = kma  K = constant of proportionality = 1
Term
 F = v♦m/♦t
Definition
 This form of Newtons second law is used when there is a continuous loss or gain of mass of an object
Term
 IMPULSE
Definition
 The impulse of a force is the the force x the time for which the force acts.   Impulse = Ft Ft = ♦(mv) This unit is usually Ns-1
Term
 FORCE TIME GRAPHS
Definition
 Rearranging Newtons second law gives: F = mv - mu/t The area under a force - time graph gives the change of momentum or impulse of the force
Term
 IMPACT FORCES - STATIONARY
Definition
 If something is initially stationary and the impact causes it to accelerate to v , the gain of momentum will be mv so the force of the impact will be F = change in momentum / contact time = F = mv / t
Term
 IMPACT FORCES - CHANGING VELOCITY
Definition
 If object is moving with velocity u and the impact changes it's velocity to v the change in momentum of the ball is mv-mu so impact force = F = change of momentum/contact time = mv-mu/t
Term
 SAFETY
Definition
 Crumple zones, seatbelts, and airbags are all designed to lessen the impact force on people. This happens by increasing the time  which decreases the acceleration/deceleration which lowers the impact force
Term
 FORCE - TIME GRAPHS FOR IMPACTS
Definition
 Variation of impact forces can be recorded using a force sensor which is connected with long wires to an object. Equal and oppositte forces act on object so variation of force with time is displayed. Average force = change of momentum/contact time
Term
 REBOUND IMPACTS
Definition
 When a ball hits a wall it's momentum changes direction due to impact. Velocity and momentum are in the opposite direction if the ball hit the wall straight up; the momentum then has the opposite sign
Term
 REBOUND IMPACTS - CHANGE SPEED
Definition
 If the ball hits the wall with initial speed u, and rebound with speed v in the opposite direction then towards the wall the momentum would be +mu and away is -mv this means the impact force will be  Force = (-mv) - (+mu) / t
Term
 IF THERE IS NO LOSS OF SPEED ON IMPACT
Definition
 v = u so F = -2mu/t
Term
 OBLIQUE IMPACTS
Definition
 Initial direction of the ball is not perpendicular to the wall. Components of the velocity must be used. If the angle of which the impact and rebound are the same, no speed is lost. so u=v
Term
 FINAL VELOCITY OF OBLIQUE IMPACTS
Definition
 -ucosΘ
Term
 CHANGE IN MOMENTUM OF OBLIQUE IMPACTS
Definition
 -2mucosΘ
Term
 NEWTONS THIRD LAW OF MOTION
Definition
 When two objects interact, they exert equal and opposite forces on each other
Term
 THE PRINCIPLE OF CONSERVATION OF MOMENTUM
Definition
 For a system of interacting objects, the total momentum remains constant, provided no external force acts on the system.
Term
 CHANGE OF MOMENTUM OF TWO COLLIDING OBJECTS
Definition
 They collide then seperate.  Momentum of each object changes. Equal and opposite forces exerted on each other when in contact so equal and opposites change in momentum.
Term
 EQUAL AND OPPOSITE CHANGES IN MOMENTUM
Definition
 One object gains momentum and the other object loses momentum
Term
 FINAL MOMENTUM
Definition
 total final momentum = total initial momentum
Term
 COLLIDING OBJECTS TICKING TOGETHER
Definition
 They have the same final velocity
Term
 TESTING CONSERVATION OF MOMENTUM
Definition
 Mass of trolleys measured before the test. Trolley A is pushed towards B at a constant velocity. They both stick on impact. Computer records change in velocity.  Measurements should show that (mb+ma)V = ma ua
Term
Definition
 If initial momentum of one object is exactly equal and opposite to that of the other object, the total momentum after the collision will be zero because they cancel out.
Term
 VECTOR NATURE OF MOMENTUM
Definition
 If the final momentum is in the other direction to the first object then it will be -. if it's in the same direction it will be +
Term
 CRASH BARRIERS
Definition
 Stop vehicles from entering the opposite carriageway. Strongest barrier are designed to ithstand the impact of a 38 tonne heavy good s vehicle at an angle of 20º and at 40mph
Term
 ELASTIC
Definition
 Elastic - loses no kinetic energy. e.g a ball will have the same amount of kinetic energy before the impact and after the impact. NO LOSS OF KINETIC ENERGY
Term
 INELASTIC COLLISIONS
Definition
 Lose kinetic energy. Colliding objects may stick together
Term
 PARTIALLY INELASTIC COLLISION
Definition
 Colliding objects move apart and have less kinetic energy after the collision than before.
Term
 KINETIC ENERGY AFTER/BEFORE A COLLISION
Definition
 EK = 1/2 mv2
Term
 KINETIC ENERGY IMMEDIATELY BEFORE IMPACT
Definition
 Loss of potential energy = mgH
Term
 KINETIC ENERGY IMMEDIATELY AFTER IMPACT
Definition
 Gain of potential energy = mgh
Term
 HEIGHT RATIO
Definition
 h/H Gives the fraction of the inital energy that is recovered as kinetic energy after the collision.
Term
 MOMENTUM
Definition
 Always conserved in collisions. Energy is always conserved, but it may be transferred into other forms
Term
 EXPLOSIONS
Definition
 Two objects fly apart - recoil from each other with equal and opposite amounts of momentum -move away in opposite directions.
Term
 RATIO OF SPEED WITH MASS
Definition
 Ratio of speed is the inverse to the mass ratio
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