1、动量,Momentum,A famous debate about movement,In physics history, there is a famous debate about movement. In the 17th century, scientists were trying to find a common physical quantity as a measure of the movement. Some people put that the product of the mass and velocity(速度) of the object should meas
2、ure the movement. Descartes is the most famous scientist of them. He put forward a principle that the amount of movement in the universe is conserved.,put forward 提出,建议put forward a suggestion,Newton agreed with it and studied further. Later this principle developed as the Law of conservation of mom
3、entum. While other people argued that the product of its mass and the square（平方） of its velocity should be the measure of the movement. Germany scientist Leibniz believed “mv” didnt follow the Law of free fall. This theory later developed as kinetic energy(动能).,Some Words about physics,momentum 动量 m
4、ass 质量 velocity 速度 speed 速率 force 力 gravity 重力 energy 能量 kinetic energy 动能,gravity n. 1.严肃庄重 say with sudden gravity 2.严重性 重要性 the gravity of the situation,internal energy 内能 mechanical energy 机械能 pressure 压力,压强 work 功 power 功率 law of conservation of energy 能量守恒定律 the Newton second law 牛顿第二定律 the th
5、eory of relativity 相对论,momentum（动量）,Momentum is the product（乘积） of the mass and velocity(速度) of an object. For example, a heavy truck moving quickly has a large momentumit takes a large force（力） to get the truck up to this speed, and it takes a large force to bring it to stop. If the truck were ligh
6、ter, or moving more slowly, then it would have less momentum. Like velocity, momentum also possesses a direction.,For example, a model airplane of 1 kg, traveling due north at 1 m/s in straight and level flight, has a momentum of 1 kgm/s due north measured from the ground.,the law of conservation of
7、 momentum,In a closed system (one that is not acted on by outside forces), the total momentum is conserved（不变的）. This fact is known as the law of conservation of momentum, which is implied by Newton second law.,act on 对.起作用，按照.行动 act on sbs advise,Suppose, for example, that two objects interact. Bec
8、ause of the third law, the forces between them are equal and opposite. If the objects are numbered 1 and 2, the second law states that:,This law holds no matter how many the forces are. Similarly, if there are several objects, the total change in momentum is zero. It can also be used in the theory o
9、f relativity.,F1=F2 m1a1= m2a2 m1a1 t=m1v1= m2a2t= m2v2 p1= p2 p1+p2 =o,Driving and Momentum,For example, when you have a large truck and a small car traveling at the same speed, the large truck is harder to stop because it has a bigger mass, and therefore a bigger momentum. If two cars with differe
10、nt masses crash head on into each other, the car with less mass will suffer more damage than the car with more mass. The car with the smaller mass is unable to withstand(抵挡) the impact of the other car because the car with more mass has more momentum.,Airbags(安全气囊) can protect the passengers and drivers from hitting the windshield(挡风玻璃).It can decrease the force of impact.,
