Physics of grade two (about force) The lovely Fuwa is having a sports match. The following is the statement about these scenes ..（ ） A when swimming, the force of the hand on the water keeps Beibei moving forward When B Beibei and Nini rowed, the rowing boat received a forward force, which had no force object When playing volleyball, Nini changed the shape of volleyball and the movement state of volleyball When playing football, the foot gives the ball a kick, and then the ball gives the foot a kick What? Why? Why is c good?

Physics of grade two (about force) The lovely Fuwa is having a sports match. The following is the statement about these scenes ..（ ） A when swimming, the force of the hand on the water keeps Beibei moving forward When B Beibei and Nini rowed, the rowing boat received a forward force, which had no force object When playing volleyball, Nini changed the shape of volleyball and the movement state of volleyball When playing football, the foot gives the ball a kick, and then the ball gives the foot a kick What? Why? Why is c good?

C
A wrong, because when swimming, it is the force of water on Fuwa that makes it move forward, not the hand on water
B wrong, a force can't be without an object
D wrong, because the force from the foot to the ball and the force from the ball to the foot are the same, we can't say "later"
You think, when playing volleyball, Nini exerts a force on volleyball. The deformation may be very small, but it must exist. After applying the force, the direction of volleyball movement must also change. So it changes both the shape and the movement state

Summarize all the knowledge and concepts of motion and force, focus on how to move out of multiple points when the object is stressed, analyze the complete from simple to difficult, copy shameful

Second grade does not need to master variable speed linear motion (may require average speed, total distance divided by total time)
Uniform linear motion: the object moves in a straight line, and the displacement is equal in any equal time interval. The popular point is that the direction of motion does not change, and the speed does not change. The difficulty is to choose the reference object, that is, to see what object is relative to, in fact, for what motion is to take what as the reference object
Force must first know that the effect is mutual, three elements: action point, direction, size
Secondly, distinguish the interaction force and the balance of two forces. There are two objects under force in the interaction force. For example, if a heavy object is placed on a horizontal table, the supporting force of the table to the heavy object and the pressure of the heavy object on the table are the interaction force. There is only one object under force in the balance of two forces. For example, the gravity of the heavy object (the earth has gravity on the heavy object) and the supporting force of the table to the heavy object are the balance of two forces
Physics in grade two is not difficult
A rope pulls a big iron ring, which is covered with two small iron rings (movable). The friction force of the big iron ring is m, the friction force of the two small iron rings is m, and the mass of the big iron ring is F. when the two small iron rings slide in a straight line with the center of the big iron ring, the pulling force of the rope can be calculated (possible difficulties)
When the small ring slides down to the position mentioned in the question, it is subject to the vertical upward sliding friction f given by the big ring. According to the interaction of forces, the small ring gives the big ring a vertical downward sliding friction, which is also F. similarly, the other small ring also gives the big ring a vertical downward sliding friction, which is also f, so the big ring is subject to four forces: the vertical upward pulling force, The vertical downward gravity and two vertical downward sliding friction, so it's M + 2F

After the kicking football hit the wall, it left a round spot on the wall, indicating that the force can change the shape of the object______ After touching the wall, it is bounced back, indicating that the force can also change the shape of the object______ ．

After the kicking football touches the wall, it leaves a round spot on the wall, which indicates that the shape of the football has changed, that is, the force has changed the shape of the object; when it touches the wall, it is bounced back, which indicates that the force has changed the movement state of the football

Physics in the second grade of junior high school
A car is driving at a constant speed on the Guangzhou Shenzhen Expressway. The driver of the car looks at his watch at the place a as shown in the figure, and the time is exactly 8 o'clock. When the car is at the place B, he looks at his watch again, and the time is 8:54?
Photo a: the sign says that it's still 100km to Shenzhen
Photo B, the sign says. It's 19km to Shenzhen
The answer is a process

Analysis:
1. The process from a to B takes 54 minutes, and the distance between AB is 100-19 = 81 km,
Therefore, the driving speed is 81 / (54 / 60) = 90 km / h,
2. It will take 19 / 90 hours