Bài giảng Vật lí 10 - Momentum

Quý Thịnh (HNUE)IGCSE1Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)Quý Thịnh (HNUE)IGCSE2Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)AimsDefine momentum.Describe experiments to demonstrate the principle of conservation of momentumState and use the principle of conservation of momentum to solve problems.Understand the action of rocket and jet engines.State the relationship between force and rate of change of momentum and use it to solve problems. Use the definition of impulse to explain how the time of impact affects the force acting in a collision.Quý Thịnh (HNUE)IGCSE3Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)Main contentConservation of momentumExplosionsRockets and jetsForce and momentumSport: impulse and collision timePractical work: Collision and momentum Quý Thịnh (HNUE)IGCSE4Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 1. Definition of momentumMomentum is a useful quantity to consider when bodies are involved in . and collisionsexplosionsQuý Thịnh (HNUE)IGCSE5Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 1. Definition of momentumIt is defined as the mass of the body .. by its velocity and It is measured in kilogram metre per second (kg m/s) or newton second (N s).multipliedQuý Thịnh (HNUE)IGCSE6Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 2. Practical workWhat is the momentum before the collision and after it in each case?Quý Thịnh (HNUE)IGCSE7Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 2. Practical WorkMass ( kg)Velocity (m/s)Momentum ( Ns)Before collisions ( rest ) Quý Thịnh (HNUE)IGCSE8Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 2. Practical work Mass ( kg)Velocity (m/s)Momentum ( +).v(Ns)After collisions (and together ) Quý Thịnh (HNUE)IGCSE9Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 2. Practical WorkMass ( kg)Velocity (m/s)Momentum ( Ns)1234Before collisions ( =2 kg rest ) 2080406020202020Quý Thịnh (HNUE)IGCSE10Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 2. Practical work Mass ( kg)Velocity (m/s)Momentum ( +).v(Ns)3456After collisions (and together ) 20,01406079,986,67101213.33Quý Thịnh (HNUE)IGCSE11Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 3. Conservation of momentum When two or more bodies act on one another, as in a collision, the total momentum of the bodies remains , provided no external forces act (e.g. friction).This statement is called the principle of conservation of momentumconstantQuý Thịnh (HNUE)IGCSE12Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 3. Conservation of momentum Example: Suppose a truck of mass 60 kg moving with velocity 3 m/s collides and couples with a stationary truck of mass 30 kg. The two move off together with the same velocity v which we can find. Quý Thịnh (HNUE)IGCSE13Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 3. Conservation of momentum Solution: Total momentum before is (60 kg × 3 m/s) + (30 kg × 0 m/s) = 180 kg m/sTotal momentum after is (60 kg + 30 kg) × v = 90 kg × v Since momentum is not lost 90 kg × v = 180 kg m/s or v = 2 m/s Quý Thịnh (HNUE)IGCSE14Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 4. Explosions Momentum is a vector since it has both .. and . Momentum is conserved in an explosion such as occurs when a rifle is fired. magnitude directionQuý Thịnh (HNUE)IGCSE15Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 4. Explosions Before firing, the total momentum is . since both rifle and bullet are at ... During the firing the rifle and bullet receive .. but .. amounts of momentum so that the total momentum after firing is zero. oppositeequalrestzeroQuý Thịnh (HNUE)IGCSE16Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 3. Explosions For example: If a rifle fires a bullet of mass 0.01 kg with a velocity of 300 m/s. Find velocity of rifle Solution: Forward momentum of bullet = 0.01 kg × 300 m/s = 3 kg m/s Backward momentum of rifle = 3 kg m/s If the rifle has mass m, it recoils (kicks back) with a velocity v such that mv = 3 kg m/s Taking m = 6 kg gives v = 3/6 m/s = 0.5 m/s. Quý Thịnh (HNUE)IGCSE17Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 4. Rockets and jetsIn both, a high-velocity stream of hot gas is produced by burning fuel and leaves the exhaust with large momentum. The rocket or jet engine itself acquires an forward momentum equalQuý Thịnh (HNUE)IGCSE18Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 5.Force and momentum If a steady force F acting on a body of mass m increases its velocity from u to v in time tQuý Thịnh (HNUE)IGCSE19Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 5.Force and momentum We also have: Therefore F.t = m.v − m.u Where m.v is the final momentum, m.u is the initial momentum and F.t is called the . impulseQuý Thịnh (HNUE)IGCSE20Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 6. Sport: impulse and collision time The force applied then acts for a longer time, the impulse is .. and so also is the gain of momentum (and .) of the object greatervelocityQuý Thịnh (HNUE)IGCSE21Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 7. ProblemDelphine hits a 0.050-kg golf ball, giving it a speed of 75 m/s. What impulse does she impart to the ball?Quý Thịnh (HNUE)IGCSE22Momentum IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,) 7. ProblemSolution: Because the impulse equals the change in momentum It is understood that the ball was initially at rest, so its initial speed was 0 m/s. Given: m=O.O50 kg v=75m/s So The impulse = (0.050 kg x 75 m/s) = 3.8 kg. m/s