物理牛顿定律英文版

1、1. Who was the scientist who gave us the Laws of Motion? Answer: Sir Isaac Newton 2. How many Laws of Motion are there? Answer: three 3. What is another name for the first law of motion? Answer: Law of Inertia 4. Which law explains why we need to wear seat belts? Answer: First Law of Motion One day

2、,Stephen Su was driving a motorcycle on the street. Meanwhile, David was driving a trunk at a fast speed.Stephen Su did not stop in time as soon as the traffic light turned red.David could not control the van and collided with Stephen.The remaining question is ,even though Stephen slammed on the bra

3、ke, the accident happened anyway. What caused this tragedy?According to Newtons first law, an object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Newtons first law of motion牛顿第一定律: Every body continues in its state of uniform m

4、otion or rest unless acted up on by an external forceApplication of the Newtons first lawSafety beltsAny passengers in the car will also be decelerated to rest if they are strapped to the car by seat belts. Being strapped tightly to the car, the passengers share the same state of motion as the car.

5、As the car accelerates, the passengers accelerate with it; as the car decelerates, the passengers decelerate with it; and as the car maintains a constant speed, the passengers maintain a constant speed as well. A disk and a hoop of the same mass M and radius R roll without slipping across a horizont

6、al floor. Both the disk and the hoop are moving with velocity v when the floor starts to slope upward. Which statement is correct? ( )(a) The disc makes it to a greater height than the hoop.(b) The hoop makes it to a greater height than the disk.(c) Both the disk and the hoop make it to the same hei

7、ght.A disk and a hoop of the same mass M and radius R roll without slipping across a horizontal floor. Both the disk and the hoop are moving with velocity v when the floor starts to slope upward. Which statement is correct? ( b )(a) The disc makes it to a greater height than the hoop.(b) The hoop ma

8、kes it to a greater height than the disk.(c) Both the disk and the hoop make it to the same height.Example 1: Consider a crate being pulled along a horizontal, frictionless floor. A rope is tied around it and a man pulls on the rope with a force of T. T is the tension in the rope. What happens to th

9、e crate? These forces are shown on the free body diagram above. We have drawn in all the forces acting on the object. The net force is the vector sum of these forces.Fnet = F = T + n + wFnet, x=F x=Tx+n x+ w xFnet,y =Fy=Ty+ ny+ w yn = w Newtons Second Law tells us that rate of increase (or decrease)

10、 in the speed of something which is moving is proportional to the force acting on it. Imagine that you are riding a bicycle along a perfectly smooth and level road and you decide to stop pedaling. If there is a strong wind pushing against you, you will stop completely in a shorter time than you woul

11、d if the wind was light. Now that we know Newtons Laws of Motion, how do we apply them? How can they let us predict the motion of an object if we know all the forces acting upon it? How can they let us predict the forces on an object if we know its motion?FORCE = MASS times ACCELERATION or Kobes car

12、, which weighs 1,000 kg, is out of gas. Kobe is trying to push the car to a gas station, and he makes the car go 0.05 m/s2. Using Newtons Second Law, you can compute how much force Kobe is applying to the car. Answer = 50 newtons Example 2: This particular example is stated in terms of weighing a fi

13、sh in an accelerating elevator. It is also fun to think of weighing yourself in an accelerating elevator. When does an elevator accelerate upwards? When does an elevator accelerate downwards? The forces acting on the fish are shown in the free-body diagram. T is the tension supplied by the scale. Th

14、is is the value the scale reads. We may call it the apparent weight of the fish. The net force on the fish isFnet = T - mgThe net force is (always!) equal to the mass times the acceleration. This fish is moving along with the elevator. In this diagram we have taken the acceleration to be up so it is

15、 positive.Fnet = T - m g = m a T = m g+ m aT = m (g + a)While the elevator accelerates upward, the apparent weight of the fish is greater than its true weight, mg. The forces on the fish are again shown in the free-body diagram Fnet = T - mgThe net force is (always!) equal to the mass times the acce

16、leration. This fish is moving along with the elevator. Now the acceleration to be up so it is negative.Fnet = T - m g = m ( - a ) T = m g - m aT = m (g - a)While the elevator accelerates downward, the apparent weight of the fish is less than its true weight, mg.1. Which law says that force is equal to mass times acceleration (F=MA)? Answer: Second