A student is holding a small umbrella in the rain. The radius of the edge of the umbrella is R and higher than the horizontal ground h. When the umbrella rotates at an angular speed W, the umbrella throws out from the edge of the umbrella and forms a circle on the ground. What is the radius of the circle?

A student is holding a small umbrella in the rain. The radius of the edge of the umbrella is R and higher than the horizontal ground h. When the umbrella rotates at an angular speed W, the umbrella throws out from the edge of the umbrella and forms a circle on the ground. What is the radius of the circle?

V=W*R
H=1/2gt^2
s=VRt
Radius ^ 2 = R ^ 2 + S ^ 2

There is a rotating turntable. After a person walks from the edge of the turntable to the center of the turntable, what is the change in the linear speed of the turntable?

Assuming that people have static friction with the plate and do not lose energy (no relative displacement), the angular velocity is the same as that of the turntable. People are subjected to Coriolis force and turn in the same direction as the plate, so they give the plate a reverse force. But what you give me is what happens after I get to the center, so there is no force analysis. Starting from the conservation of angular momentum, people and plates

After learning the knowledge of friction, students already know that sliding friction is related to the roughness of the contact surface between objects and the pressure However, Xiao Ming always felt that the sliding friction should also be related to the size of the contact area. He guessed: "the larger the contact area, the greater the sliding friction." so he found a rectangular wooden block (each surface has the same roughness) . spring dynamometer. Long board. Then, how should he use these equipment to verify whether his conjecture is correct? Please write down his experimental steps: ①: ②: analysis and comparison:

Experimental steps: ① when the wood block is placed horizontally, pull the wood block with a spring dynamometer at a uniform speed, read out the tension F, and record it in the pre-designed table; ② When placing the wood block on the side, pull the wood block with a spring dynamometer at a uniform speed, read out the tension F, and record it in the pre-designed table. Analysis and comparison: place the wood block flat and on the side

The effect of friction force is not only the roughness of contact surface and pressure Other factors affecting friction, such as movement speed

The main factors affecting the sliding friction are
1) Roughness of contact surface
2) Positive pressure
3) Relative velocity between and object
As for the third point, you can test it by experiment

When the roughness of the contact surface is certain, the friction increases with the increase of pressure

According to you, it should be to measure the relationship between dynamic friction and positive pressure
Put a wooden block on the board, pull it with a spring dynamometer at a uniform speed, record the value, put a weight on it, pull it with a spring dynamometer, record the value, add the weight, pull it again, and compare the data in the list

When the roughness of the contact surface and the pressure are constant, is the sliding friction related to the tensile force? The greater the tension, the greater the friction? Whether, if yes, then it is refuted that "the sliding friction is related to the pressure and the roughness of the contact surface"

. if an object moves or stands still at a constant speed under a certain tension and friction. The force on the object is friction = tension. If it does not move at a constant speed, it is tension = resistance.. there are many factors. Then if the tension is greater, the friction is greater. If it is static friction, and under the condition of less than the maximum static friction