"Kinetic Energy and Kinetic Energy Theorem" Law of Conservation of Mechanical Energy PPT high-quality courseware

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"Kinetic Energy and Kinetic Energy Theorem" Law of Conservation of Mechanical Energy PPT high-quality courseware

Part One: Core Competency Goals

physical concepts

Understand the concept of kinetic energy and the kinetic energy theorem.

scientific thinking

Experience the process of establishing the concept of kinetic energy, improve your deductive reasoning ability, and be able to use kinetic energy theorem to solve practical problems in mechanics.

Scientific attitude and responsibility

Perceive the application of kinetic energy theorem in life and improve the ability to combine theory and practice

Kinetic energy and kinetic energy theorem PPT, part 2 content: pre-class learning

Knowledge point 1: Expression of kinetic energy

As shown in Figure A, it is a chariot used to attack the city gate in ancient wars. The chariot is equipped with a log with a large mass. Many soldiers push it and hit the city gate at a very high speed, breaking the city gate easily. . When the mass of the log is very large and the speed is very high, what energy is used to increase the energy of the log?

As shown in Figure B, when people use a hammer to hit a stone, why do they use a larger hammer and swing it high? How can this increase the power of the hammer when it hits the stone?

1. Definition: In physics, the quantity "__________" is used to represent the kinetic energy of an object.

2.Expression

Ek=_______.

3.Unit

In the International System of Units it is _______, and its symbol is ______. 1 kg(m/s)2＝1 N•m＝1 J.

[Thinking and Judging]

(1) All moving objects have kinetic energy. ( )

(2) For an object of a certain mass, when the kinetic energy changes, the speed will definitely change, but when the speed changes, the kinetic energy does not necessarily change. ( )

(3) An object with constant kinetic energy must be in equilibrium. ( )

(4) The kinetic energy of an object in uniform circular motion remains unchanged. ( )

Learned kinetic energy in junior high school

The energy an object possesses due to motion is called kinetic energy.

Objects with the same mass, the greater the moving speed, the greater the kinetic energy; objects moving at the same speed, the greater the mass, the greater the kinetic energy.

The "three properties" of kinetic energy

(1) Relativity: Choose different reference systems, the speed of objects is different, and the kinetic energy is also different. Generally, the ground is used as the reference system.

(2) Scalar: Kinetic energy is a scalar quantity and has no direction.

(3) Instantaneity: kinetic energy is a state quantity.

Knowledge Point 2 Kinetic Energy Theorem

1. Derivation: As shown in the figure, the mass of the object is m. Under the action of a constant force F in the same direction of motion, a displacement l occurs, and the speed increases from v1 to v2. The work done by the force F in this process is W.

2. Content: The work done by a force on an object during a process is equal to the ______________ done by the object during the process.

3.Expression: W=__________. The work "W" in the kinetic energy theorem refers to the work done by the resultant force.

4. Scope of application: It is suitable for both __________ work and ________ work; it is suitable for both ________ sports and ________ sports.

[Thinking and Judging]

(1) When the combined force does positive work, the kinetic energy of the object may decrease. ( )

(2) The net external force on a moving object is zero, so the kinetic energy of the object must remain unchanged. ( )

(3) When an object moves at a variable speed, the total external force must not be zero, and the kinetic energy must change. ( )

(4) If the work done by the net external force on the object is zero, then the net external force must be zero. ( )

(5) When the net external force of an object does work, its speed must change. ( )

Kinetic energy and kinetic energy theorem PPT, part three: core exploration

Core Point 1: Understanding of kinetic energy and kinetic energy theorem

1. Three relationships between kinetic energy and speed

(1) Numerical relationship: Ek=12mv2. When the mass is constant, the greater the speed v, the greater the kinetic energy Ek.

(2) Instantaneous relationship: Both kinetic energy and speed are state quantities, and they have an instantaneous correspondence.

(3) Change relationship: kinetic energy is a scalar quantity and speed is a vector quantity. When the kinetic energy of an object with a certain mass changes, the speed (size) of the object must change; when the speed changes, it may only be a change in the direction of the speed, and the object The kinetic energy of may remain unchanged.

2. Understanding of kinetic energy theorem

(1) Two understandings of "force"

① "Force" can be various forces such as gravity, elasticity, friction, etc. They can act at the same time or not at the same time.

② "Force" can be either a constant force or a variable force.

(2) The three relationships reflected by “=" in the formula

3. The relationship between the work done by the resultant force and the change of kinetic energy

[Examination Cases]

[Example 1] Regarding the relationship between the net external force on a moving object, the work done by the net external force, and the change in kinetic energy, the following statement is correct ()

A. If the net external force is zero, then the work done by the net external force must be zero.

B. The work done by the total external force is zero, then the total external force must be zero

C. The more work the combined external force does, the greater the kinetic energy must be.

D. The kinetic energy does not change, then the net external force of the object must be zero.

[For training 1] (Multiple choice) An object with mass m starts from rest on a smooth horizontal ground under the action of horizontal force F. After advancing a certain distance, the speed is v, and then moving forward a certain distance so that The speed of the object increases to 2v, then ()

A. The speed increment of the second process is equal to the speed increment of the first process

B. The kinetic energy increment of the second process is 3 times the kinetic energy increment of the first process.

C. The work done by the combined external force in the second process is equal to the work done by the combined external force in the first process.

D. The work done by the combined external force in the second process is equal to twice the work done by the combined external force in the first process.

Core Point 2 Application of Kinetic Energy Theorem

1. Things to note when applying the kinetic energy theorem to solve problems

(1) The displacement and velocity in the kinetic energy theorem must be relative to the same reference system. Generally, the ground or an object stationary relative to the ground is the reference system.

(2) The expression of the kinetic energy theorem is a scalar equation, but when applying the kinetic energy theorem, it is necessary to clarify the positive and negative work done by each force.

2. Some explanations on the kinetic energy theorem

[Examination Cases]

Example 2 The length of BC is s = 5 m, the orbit CD is long enough, and the inclination angle θ = 37°. The heights of points A and D from the orbit BC are h1 = 4.30 m and h2 = 1.35 m respectively. Now let the small slider with mass m be released from rest at point A. It is known that the kinetic friction factor μ = 0.5 between the small slider and the track BC, the gravity acceleration g is 10 m/s2, sin 37° = 0.6, cos 37° =0.8. beg:

(1) The speed of the small slider when it first reaches point D;

(2) The distance between the final stop position of the small slider and point B.

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Update Time: 2024-10-06

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