"Overweight and Weightlessness" Newton's Laws of Motion PPT download

Description

"Overweight and Weightlessness" Newton's Laws of Motion PPT download

The first part of the content: [Learning literacy·clear goals]

Physical concepts: 1. Know what overweight and weightlessness are. 2. Know the conditions that produce overweight and weightlessness.

Scientific thinking: Be able to analyze and solve the problems of overweight and weightlessness based on Newton's second law.

Overweight and weightlessness PPT, part 2: independent preview and exploration of new knowledge

1. Overweight phenomenon

1. Overweight phenomenon: The pulling force of an object on the suspended object (or the pressure on the support) ____ the gravity of the object.

2. Conditions for production: The object has an acceleration of ________, which is the same as the speed and direction of the object.

3. Type of exercise: Overweight objects doing upward ________ or downward ________.

2. Weightlessness phenomenon

1. Definition: The pulling force of an object on a suspended object (or the pressure on a support object) _______ the phenomenon of gravity exerted by an object.

2. Conditions for production: The object has _______ acceleration.

3. Type of motion: Weightless objects move upward _______ or downward _______.

4. Complete weightlessness

(1) Definition: A state in which the _______ (or pressure on the support) of the object on the suspended object is equal to zero.

(2) Conditions for production: The vertical downward acceleration of an object is equal to _______.

(3) All projectile motion, regardless of resistance, is in a _________ state.

Basic self-test

1. Think and judge (mark “√” if correct, “×” if incorrect)

(1) When an object is in an overweight state, it must move upward. ( )

(2) When an object is in an overweight state, it may move downward. ( )

(3) An object thrown vertically upward is in an overweight state during its ascent. ( )

(4) As long as the object moves downward, it will cause weightlessness. ( )

(5) When an object is completely weightless, the pressure on the support surface that supports it is zero. ( )

(6) When an object is completely weightless, it is not affected by gravity. ( )

2. Which of the following statements is correct ()

A． Only objects that are moving upward can be in a state of overweight

B． Overweight means an increased gravitational force on an object

C. When an object is in a super-heavy state, the Earth's gravitational pull on it becomes stronger

D. The gravitational force on an object remains unchanged when it is overweight

3. A diver jumps into the air from a 10 m platform, moves upward for a certain distance to reach the highest point, and then falls freely into the pool. Regardless of air resistance, the following statements about the rising and falling processes of athletes leaving the springboard in the air are correct: ()

A． The ascent process is in a state of overgravity, and the fall process is in a weightless state.

B． The ascent process is in a state of weightlessness, and the fall process is in a state of overgravity.

C. Both the ascent and descent processes are in an overweight state

D. Both the ascent and descent processes are in a state of complete weightlessness.

Overgravity and weightlessness PPT, the third part: cooperative exploration to overcome difficult problems

Overweight

1. Emphasis and emphasis

(1) Actual weight: the actual gravity of the object. The gravity exerted by an object will not change due to changes in the object's motion state.

(2) Apparent weight: When a spring dynamometer or platform scale is used to measure the gravity of an object, the indication of the spring dynamometer or platform scale is called the apparent weight of the object. When the object and the spring dynamometer remain stationary or move at a constant speed, the apparent weight is equal to the actual weight; when there is acceleration in the vertical direction, the apparent weight is no longer equal to the actual weight.

2. Overweight

(1) Overweight phenomenon: The pulling force of an object on the suspended object (or the pressure on the supporting object) is greater than the gravity of the object.

(2) The reason for overweight: When the object has a vertical upward acceleration a, the supporting force of the support on the object (or the pulling force of the suspension rope) is F. According to Newton's second law, we can get: F-mg=ma. So F=m(g+a)>mg. According to Newton’s third law, the pressure of the object on the support (or the tension on the suspension rope) F′>mg.

(3) Dynamic characteristics of overweight:

Overweight accelerates upward and decelerates downward. The acceleration direction is upward (or has an upward component).

[Example 1] A person standing on an elevator lifts a fish with a mass of 1 kg using a spring dynamometer. The reading of the spring dynamometer is 12 N. The person’s weight is 750 N. Then his weight on the elevator floor The pressure is (g is 10 m/s2)()

A． 750 N B. 762N

C. 900N D. 912N

Idea suggestion: The acceleration of the elevator, people and fish are the same, and the movement of the person can be analyzed from the fish. In addition, the pressure a person exerts on the floor must take into account the fish he is holding.

D. The gravity of a 1 kg fish is 10 N, and the pulling force of the spring dynamometer is 12 N. It can be seen that the resultant force on the fish is F fish = (12-10) N = 2 N. According to Newton's second law It can be seen that the acceleration of the fish at this time is 2 m/s2 and the direction is upward. This also indicates that the elevator and the people in the elevator are also moving upward with acceleration. Considering the people and the fish as a whole, we can get N-(M+m)g= (M+m)a, N is the upward force exerted by the floor on the person, and the reaction force exerted by the person on the floor is equal to N and directed downward. The calculation shows that N=912 N, so D.]

regular method

Two tips for understanding the phenomenon of being overweight

(1) When an object is in an overweight state, its actual weight (that is, the gravity it exerts) does not change, but its apparent weight changes, and the apparent weight increases by ma compared to its actual weight.

(2) The factor that determines the overweight of an object is that the object has upward acceleration, regardless of speed, that is, the object can accelerate upward or decelerate downward.

weightlessness

1. Understanding the phenomenon of weightlessness

(1) From the perspective of force: when the object is weightless, the pulling force of the vertical suspension rope (or dynamometer) or the supporting force of the horizontal support surface (or platform scale) is less than gravity, as if gravity has become smaller. It is precisely because of this , defining this phenomenon as "weightlessness".

(2) From the perspective of acceleration: According to Newton's second law, the acceleration direction of an object in a weightless state is downward (a≤g, as shown in the figure). This is the condition for the object to be weightless, and it is also the basis for judging whether the object is weightless. in accordance with.

2. Understanding of complete weightlessness

When the object is in a state of complete weightlessness (a = g), gravity will generate all acceleration and no pressure (as shown in the figure). All physical phenomena caused by gravity will completely disappear, such as the failure of the balance and the failure of objects immersed in water. No longer subject to buoyancy, the liquid column no longer produces pressure, etc.

[Example 2] A person with a mass of 60 kg stands on a scale in an elevator. As shown in the figure, what are the readings of the scale when the elevator performs the following movements? (g is taken as 10 m/s2)

(1) The elevator rises at a constant speed;

(2) The elevator accelerates downwards at a uniform acceleration of 3 m/s2.

Ideas: ①The reading on the scale corresponds to the amount of pressure a person is feeling.

②The conversion object method can be used to analyze human forces.

regular method

How to deal with overweight and weight loss problems

(1) Use Newton's second law to analyze equations. Use the direction of acceleration as the positive direction to formulate Newton's second law equation. After obtaining the result, pay attention to using Newton's third law to transform it into the desired conclusion. Also pay attention to distinguishing between acceleration and acceleration. direction and speed direction.

(2) When dealing with connected body problems, such as changes in the indications of dynamometers and platform scales, changes in the motion state of one of the objects (or part of the object) will affect whether the system maintains its original equilibrium state. To judge the problem, you can analyze and judge based on the overweight and weightlessness phenomena that occur at the center of gravity of the system.

Overweight and weightless PPT, Part 4: Complying with standards and solidifying double bases in court

1. Which of the following judgments about overweight and weightlessness is correct ()

A． When an object moves at a variable speed, it must be in a state of overweight or weightlessness.

B． When an object moves downward, it must be in a weightless state

C. An object that is thrown vertically upward is in an overweight state

D. The object moves diagonally upward with uniform deceleration and is in a state of weightlessness.

2. Which of the following statements is correct ()

A． The gymnast is in a weightless state while holding the horizontal bar with both hands and hanging motionless in the air.

B． Trampoline athletes are weightless as they rise and fall in the air

C. A weightlifter is overweight during the period of time after lifting the barbell and not moving.

D. A swimmer is in a state of weightlessness when lying on his back and motionless on the surface of the water.

3. (Multiple choices) In an elevator that is moving at a constant speed, there is an object A with a certain mass pulled by an elongated spring and resting on the floor, as shown in the figure. It is found that A is suddenly pulled to the right by the spring. From this, it can be judged that the movement of the elevator at this time may be ()

A． Accelerate the rise B. Slow down and rise

C. Accelerate the descent D. Slow down and descend

4. A person can lift a maximum weight of 60 kg on the ground. When this person stands in an elevator that accelerates upward at an acceleration of 5 m/s2, what is the maximum mass of an object that can be lifted? (g is taken as 10 m/s2)

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For more information about the "Newton's Laws of Motion Overweight and Weightlessness" PPT courseware, please click the Newton's Laws of Motion ppt Overweight and Weightlessness ppt tag.

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Update Time: 2024-11-22

This template belongs to Physics courseware Lu Ke Edition High School Physics Compulsory Course One industry PPT template

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