"Gravity and Elasticity" Interaction - Force PPT Courseware

Description

"Gravity and Elasticity" Interaction - Force PPT Courseware

Part One: Learning Objectives

1. Understand the concept and vectoriality of force, and be able to draw force diagrams. (emphasis)

2. Understand the cause of gravity, determine the magnitude and direction of gravity, and understand the concept of center of gravity. (difficulty)

3. Know the concept of deformation and be able to distinguish whether a certain deformation is elastic deformation or inelastic deformation.

4. Knowing the definition of elastic force and the conditions for its generation, you can determine whether there is elastic force between two objects and determine the direction of elastic force. (emphasis)

5. Master Hooke's law and be able to use it to solve related problems. (difficulty)

6． Explore the quantitative relationship between elastic force and spring elongation.

Gravity and elasticity PPT, part 2: exploration of new knowledge

Basic combing

1. Gravity

1. basic properties

(1)Definition: The force exerted on an object due to ______________ is called gravity.

(2) Size: G=___________.

(3) Direction: always___________.

(4) The meaning of g: acceleration of gravity, usually 9.8 m/s2.

2. center of gravity

(1) Definition: Each part of the object is affected by gravity. From the effect point of view, it can be considered that the gravitational effect on each part is _______________, which is the center of gravity of the object.

(2) Factors that determine the position of the center of gravity of an object

①The _________ of the object.

②Object___________.

(3) Determine the position of the center of gravity: ________ method.

3. Illustration of force

(1) The three elements of force: magnitude, direction and ________.

(2) Representation method: Force can be represented by directed line segments. The ________ of a directed line segment represents the magnitude of the force, the ________ represents the direction of the force, and the __________________ represents the point of action of the force.

2. Elasticity

1. Deformation: An object will change _________ or _________ under the action of force. This change is called deformation.

2. Definition: An object that is _______ will exert a force on the objects in contact with it due to its need to ____________.

3. Categories: Stress, _________ and _________.

4. Direction: (1) Pressure and support force: perpendicular to _________, pointing toward the object being pressed or supported.

(2)The tension of the rope: along the rope pointing towards the rope _______________.

3. Hooke’s Law

1. Elastic deformation: The deformation that can be ____________ after the force is removed.

2. Elastic limit: When the deformation exceeds a certain limit, after the force is removed, the object cannot ____________ the limit of its original shape.

3. Hooke's law: When a spring ____________, the elastic force F is proportional to the length x of the spring _______________, that is, F = _____________.

4. Stiffness coefficient: k in the formula F=kx is called ____________, the unit is ____________, and the symbol of the unit is ____________.

self-test

Thinking Analysis

(1) The direction of gravity can also be expressed as pointing towards the center of the earth. ()

(2) The center of gravity is the point of action of the object's gravity, and the center of gravity must be on the object. ()

(3) The book is placed on the table, and both the book and the table deform. ()

(4) There must be elastic force between objects in contact with each other. ()

(5) Within the elastic limit, if the two springs are stretched to the same length, the elastic force must be equal. ()

(6) Within the elastic limit, when the same spring is stretched by length x and compressed by length x, the magnitude of the elastic force is equal. ()

basic understanding

(1) (2019•Tonglu School-Level Monthly Examination) From the perspective of scientific methods, the introduction of the concept of "center of gravity" in physics mainly uses ()

A. Control variable method B. Equivalent alternative

C. Ideal experimental method D. Modeling methods

(2) In the picture, the contact surface in picture C is smooth, and there must be elastic force between the two balls A and B (both are stationary) ()

Tip: Choose B. To determine whether there is elastic force between balls A and B, we must rely on the two conditions for the elastic force to occur: first, mutual contact; second, elastic deformation. The contact condition is met in all four options, but it is difficult to observe whether deformation has occurred. In this case, the "hypothesis method" can be used to judge. In picture A, if ball A is taken away, ball B will be stationary, so there is no squeeze between A and B, that is, there is no elastic force between A and B; in picture B, if ball A is taken away, ball B will move to the left. motion, so there is mutual extrusion between A and B, that is, there is elastic force between A and B; in picture C, if ball A is taken away, ball B will be stationary, so there is no extrusion between A and B, that is, there is no extrusion between A and B. There is no elasticity; in picture D, there may or may not be elasticity between A and B, so option B is correct.

(3) On the earth, objects tend to move downward due to the influence of gravity. This is a natural phenomenon that we are all familiar with. But in the China Science and Technology Museum, there is such an object called a double cone, as shown in the picture. Move the double cone roller to the lower end of the guide rail, then release your hands, and the cone will automatically roll up. That is to say, the double cone can move from low to high without the action of external force, and the double cone will climb the slope. The phenomenon we see is that the double cone moves from low to high. Try to explain this phenomenon.

Gravity and Elasticity PPT, Part 3: Teacher-student interaction

The nature of gravity and the location of the center of gravity

Problem guide

As shown in the picture, the apples on the tree will fall to the ground; workers on construction sites often use heavy vertical lines to check whether the walls are vertical. Why do apples on trees always fall to the ground? Why can we use heavy vertical lines to detect whether the wall is vertical?

Key points: The object falls to the ground because of the vertical downward gravity; the vertical line can detect whether the wall is vertical, because the direction of gravity is vertical downward. When the heavy hammer is stationary, the thin thread hanging the heavy hammer The direction of the line must be along the vertical direction. If the wall is parallel to the thin line, it means that the wall is vertical and not tilted.

【Core Deepening】

1. The generation, direction, magnitude and center of gravity of gravity

The force exerted on an object due to the attraction of the earth is generally not equal to the attraction of the earth

Direction Vertically downward or perpendicular to the horizontal plane

Size G=mg

(1) At the same place, the magnitude of gravity is proportional to the mass

(2) At different locations, the gravity of the same object increases with latitude and decreases with altitude.

(3) The magnitude of gravity has nothing to do with the state of motion of the object, and has nothing to do with whether the object is subject to other forces.

2. The relationship between the center of gravity and the shape and mass distribution of the object

Key Competency 1 Understanding Gravity

(2019•Guangxi Yulin High School Grade 1 Midterm) Regarding gravity, the correct statement is ()

A. Gravity is the attraction of the earth to objects

B． Only objects at rest are affected by gravity

C. Whether the same object moves upward or downward on the earth, it is affected by gravity

D． An object is affected by gravity only when it is moving downwards

Key competency 2: Understanding of focus

Regarding the center of gravity of an object, which of the following statements is incorrect ()

A. The center of gravity of an object may not be on the object

B． When an object suspended vertically by a line is at rest, the direction of the line must pass through the center of gravity

C. When a brick is placed flat, sideways or upright, the position of its center of gravity within the brick remains unchanged.

D． When a dancer performs various graceful movements, the position of the center of gravity in the body remains unchanged.

Key Competency 3: Use core knowledge to explain life phenomena

Before the nature of gravity was clearly understood, the working people of ancient my country had relatively complex applications. An ancient pointed-bottomed pottery vase was unearthed in Banpo, Xi'an, my country. As shown in the picture, this kind of pottery vase has a large mouth and a large belly. It has two ears below the waist of the vase. The bottom is pointed. If two ropes are used to tie the two If you lift the bottle with your ears, you can get water from the well. Try to analyze how people use pointed-bottomed pottery bottles to get water from wells.

Make use of the topic

How to determine the center of gravity

(1) For an object with uniform mass distribution, the position of the center of gravity is only related to the shape of the object.

If the shape of an object is centrally symmetrical, the center of symmetry is the center of gravity. For example: solid objects such as rulers and shot put, as well as hollow objects such as basketballs and volleyballs, have their centers of gravity at the geometric center, as shown in the figure.

(2) The suspension method determines the center of gravity of a thin plate-shaped object.

Principle: When two forces are in balance, the two forces are equal in magnitude and opposite in direction.

Method: The center of gravity of a thin plate-like object can be determined by the suspension method. As shown in the figure, first hang the plate at point A. When the object is stationary, the gravity of the object and the tension of the suspension rope are on the same vertical line, so the object's The center of gravity must be on the vertical line AB passing through point A. Then hang the object at point C. In the same way, the center of gravity of the object must be on the vertical line CD passing through point C. The intersection O of AB and CD is the center of gravity of the thin plate.

[Exercise to achieve standards]

1. (2019•Xingqing School Grade Final) The following statements about gravity and center of gravity are correct ()

A. For any object with a regular shape, its center of gravity must coincide with its geometric center

B． The center of gravity of any object is inside the object and cannot be outside the object

C. Use a rope to hang an object. When the object is stationary, the center of gravity of the object is not necessarily on the extension line of the rope.

D． Gravity is caused by the gravitational pull of the earth on objects near the ground

2. As shown in the figure, a hollow uniform spherical shell is filled with water. There is a small hole directly below the ball. As the water slowly flows out of the small hole, the common center of gravity of the hollow spherical shell and the water will be ()

A. keeps falling

B． keeps rising

C. First increase and then decrease

D． First decrease and then increase

Determining the presence and direction of elasticity

Problem guide

As shown in the figure, a steel ball is placed in a measuring cup, an ordinary teacup with a large mouth and a small bottom, and a triangular beaker. The steel ball is in a stationary state at the bottom of each container in contact with the side wall. If the steel ball and each container are smooth, and the bottom of each container is in the horizontal plane, do the side walls of each container have an elastic effect on the steel ball?

Key points: When the side wall of the container is removed, the steel ball is still at rest, so the side wall of each container has no elastic effect on the steel ball.

Gravity and Elasticity PPT, Part 4: Focus on Core Competencies

Ropes, rods, springs and rubber bands can all produce elastic force, but some can change instantaneously, while others cannot; some of the magnitude of the elastic force can be calculated using Hooke's law and equilibrium conditions, while others can only be calculated based on equilibrium conditions and the laws of motion. Find out; the directions of the elastic forces are also different. The comparison is as follows:

rod

Can be subjected to both tension and pressure

The amount of deformation is tiny

It takes almost no time for the deformation to disappear or change

spring

Can be subjected to both tension and pressure

non-micro deformation

Generally, deformation changes take some time

rope

Can only bear tensile force

The amount of deformation is tiny

It takes almost no time for the deformation to disappear or change

rubber band

Can only bear tensile force

non-micro deformation

Generally, deformation changes take some time

[Exercise to achieve standards]

1. As shown in the figure, one end of an elastic rod is fixed on an inclined plane with an inclination angle of 30°, and a small ball with a gravity of 2 N is fixed on the other end of the rod. The ball is at rest, then the elastic force of the elastic rod on the ball is ( )

A. The size is 2 N and the direction is parallel to the slope upward.

B． The size is 1 N and the direction is parallel to the slope upward.

C. The size is 2 N and the direction is perpendicular to the slope upward.

D． The size is 2 N and the direction is vertically upward.

2. (Multiple choice) As shown in the figure, the gravity of objects A and B is GA=3 N and GB=4 N respectively. A is suspended from the top plate with a thin wire, and B is placed on a horizontal surface. The elastic force of the light spring between A and B is F = 2 N. Then the possible values ​​of the tension FT in the thin wire and the pressure FN of B on the ground are ()

A. 5 N and 6 N B. 5N and 2N

C. 1 N and 6 N D. 1N and 2N

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For more information about the "Interaction Forces Gravity and Elasticity" PPT courseware, please click the Interaction Forces ppt Gravity and Elasticity ppt tag.

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Update Time: 2024-10-30

This template belongs to Physics courseware People's Education Press High School Physics Compulsory Course 1 industry PPT template

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