"Circular Motion in Life" Circular Motion PPT Courseware

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"Circular Movement in Life" Circular Movement PPT Courseware

Part 1: Essential knowledge and foundation of literacy

1. The train turns

【think】

When the train turns, are the heights of the outer rail and the inner rail the same? What are the characteristics of the wheel design of the train?

Tip: When the train turns, the heights of the outer rail and the inner rail are different. The outer rail is higher and the inner rail is lower. Train wheels are designed with protruding rims.

1. Structural characteristics of train wheels: There are protruding rims on the train wheels. When the train is running, the side with the rim is in the track.

Function: Helps to fix the movement trajectory.

2. The movement characteristics of the train on the curve: circular motion, with centripetal acceleration pointing to the center of the circle.

3. Source of centripetal force: When the inner and outer rails are at the same height, the _________ of ____________ provides centripetal force.

When there is a height difference between the inner and outer rails, running at the specified speed, ____________________ provides centripetal force.

2. Cars crossing the arched bridge

3. Weightlessness in spacecraft

【think】

If an object is placed on a horizontal table, it will exert pressure on the table; if the spacecraft moves in a circle around the earth, will the objects in the spacecraft exert pressure on the spacecraft?

Tip: Objects in the spacecraft do not exert pressure on the spacecraft.

1. Centripetal force analysis: The combined force of _________ and _______________ on the astronaut provides him with centripetal force. _____=.

2. Weightless state: When v=_____, the support force of the cockpit to the astronaut is zero, and the astronaut is in a state of complete weightlessness.

4. Centrifugal movement

1. Meaning: The object flies out along the _________ or moves gradually away from the center of the circle.

2. Reason: The centripetal force suddenly disappears or _____________ provides the required centripetal force.

Circular Movement in Life PPT, Part 2: Key Competencies·Quality Formation

1. The train turns

1. The curve of the railway:

(1) If the inner and outer rails of a railway curve are the same height, the rim of the outer wheel squeezes the outer rail, causing the outer rail to elastically deform. The elastic force of the outer rail against the rim is the centripetal force of the train turning, as shown in Figure A, but The mass of the train is very large, and the centripetal force is obtained by this method. The interaction force between the rim and the outer edge is too large, and the rails and wheels are easily damaged.

(2) If the outer rail is slightly higher than the inner rail at a curve, as shown in Figure B, the direction of the rail's support force FN for the train when the train turns is no longer vertical, but points diagonally toward the curve. On the inside, the combined force of it and gravity points to the center of the circle, providing all or part of the centripetal force for the train to turn, reducing the squeeze between the rim and the outer rail.

2. The prescribed speed when the train turns:

(1) Relevant physical quantities: If the centripetal force when the train turns is completely provided by the combined force of gravity mg and support force FN, assume that the distance between the inner and outer rails is L, the height difference between the two rails is h, the turning radius of the train is R, and the train's turning radius is R. The mass is m.

(2) Theoretical analysis: According to the geometric relationship, sin θ=____ is known; from the force of the train shown in the figure, tan θ=____. When θ is very small, it is approximately believed that sin θ=tan θ, that is, ____, so F Together=mg____. According to the centripetal force formula, F = ____, so ____, v0=____. Since the quantities h, L, and R are determined after the railway track is built, the speed of the train when turning when there is no lateral pressure on the track should be a fixed value, that is, the prescribed speed.

(3)Speed ​​relationship:

① When the speed of the train when turning is v=v0, there is no lateral pressure from the wheel rim to the inner and outer rails.

②When the train turning speed v>v0, the outer rail has inward lateral pressure on the wheel rim.

③When the train turning speed v

【Think·Discussion】

Scenario: A high-speed train performs uniform circular motion when passing through the curve as shown in the figure.

discuss:

(1) What are the characteristics of the rails at the turns of high-speed trains and what forces provide centripetal force when turning? (Scientific thinking)

Tip: The rails at the turn are high on the outside and low on the inside; when turning, the centripetal force is provided by the combined force of gravity and supporting force.

(2) If the speed of a high-speed train is too high or too low when turning, which side of the track will have lateral pressure? (Scientific thinking)

Tips: ① If the speed is too high, there will be lateral pressure on the outer track.

②The speed is too small and there is lateral pressure on the inner track.

[Typical example demonstration]

(Multiple choices) When designing the turning point of the train track in the horizontal plane, it should be designed with a structure with high outer rail and low inner rail, that is, the roadbed forms a slope with high outer and low inner (as shown in the figure). The height difference between the two rails should be designed taking into account the turning radius of the rails and the speed of the train. If a turn is designed so that when a train passes at speed v, the pressure exerted on the inner and outer rails by the wheel rims on them is exactly zero. The friction between the wheels and the rails is negligible, then which of the following statements is correct ()

A. When the train passes through this curved road at speed v, the resultant direction of the forces on the train is downward along the roadbed.

B. When the train passes through this curve at speed v, the combined force of the train's gravity and the rail's support force provides a centripetal force.

C. When the speed of the train is greater than v, the outer rail exerts pressure on the rim of the wheel

D. When the speed of the train is less than v, the outer rail exerts pressure on the rim of the wheel

[Analysis] Choose B or C. When the train turns, the pressure on the inner and outer rails from the rims on them is exactly zero. The centripetal force is provided by the combined force of gravity and supporting force, and the direction points horizontally towards the center of the circle, so A is wrong and B is correct; when the speed is greater than v , the resultant force of gravity and support force is less than the required centripetal force. At this time, the outer rail exerts pressure on the wheel rim, so C is correct; when the speed is less than v, the resultant force of gravity and support force is greater than the centripetal force. At this time, the inner rail exerts pressure on the wheel rim. Apply pressure, so D is wrong.

【Literacy Training】

1. (Multiple choice) A train turning can be approximately regarded as a uniform circular motion. When the train passes at the specified speed, neither the inner or outer rails will be squeezed sideways. In order to reduce the prescribed speed of trains when turning, the railway needs to be modified. Theoretically speaking, the following measures are feasible: ()

A. Reduce the height difference between the inner and outer rails B. Increase the height difference between the inner and outer rails

C. Reduce the radius of the curve D. Increase the radius of the curve

[Analysis] Choose A or C. When the train passes through a curve at a specified speed, the combined force of the train's gravity and supporting force provides centripetal force, as shown in the figure:

2. (Multiple choices) Roads along cliffs are often called the most dangerous roads. If a car wants to pass through this curved road safely, which of the following statements is correct ()

A. If the car turns at a constant angular speed, it is safer to choose the inner circle

B. If the car turns at a constant linear speed, it is safer to choose the outer circle

C. The car is affected by gravity, supporting force and friction when turning

D. The car is affected by gravity, supporting force, friction and centripetal force when turning.

2. Cars crossing the arched bridge

1. The situation when a car passes through the highest point of an arched bridge:

As shown in the figure, assume that the mass of the car is m, the arc radius of the bridge deck is r, and the speed when the car passes the highest point of the bridge deck is v.

2. The situation when the car passes through the lowest point of the concave bridge:

As shown in the figure, the car is affected by gravity mg and the support force FN of the bridge in the vertical direction. The resultant force of these two forces provides the centripetal force for the car to move in a circular motion.

3. General ideas for dealing with circular motion mechanics problems:

(1) Determine the orbital plane and center of the circular motion of the object.

(2) Find the orbit radius based on geometric relationships.

(3) Conduct force analysis on the object to determine the source of the centripetal force.

(4) Solve the equations according to Newton's second law.

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Update Time: 2024-11-21

This template belongs to Physics courseware People's Education Press High School Physics Compulsory Course II industry PPT template

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