What Is Kinetic Energy?
The energy that an object has due to its mechanical movement.
- Chinese name
- kinetic energy
- Foreign name
- kinetic energy
- expression
- Ek = mv² / 2
- Presenter
- Corioli
- Applied discipline
- physics
- Unit
- Joule (J) for short
- The energy that an object has due to its mechanical movement.
Kinetic energy formula definition
Kinetic energy definition
- Definition: The energy that an object has due to its movement is called its kinetic energy. Its size is defined as half of the product of the mass of the object and the square of the speed.
Kinetic energy conclusion
- Therefore, objects with the same mass have a higher kinetic speed and a larger kinetic energy; objects with the same mass have a larger kinetic energy.
Kinetic energy formula
- In the physics textbook of 2013: the eighth grade of the People's Education Press (2012 edition) chapter eleven
- In classic physics:
- The kinetic energy formula is:
- Kinetic energy calculation formula
- Einstein supplemented the above formula in the theory of relativity
- The complete formula is:
- m0 is the static mass
- Kinetic energy is scalar;
- Kinetic energy is instantaneous. At a certain moment, an object has a certain speed and a certain kinetic energy. Kinetic energy is a state quantity;
- Kinetic energy is relative. For different reference frames, the speed of the object has different instantaneous values, which means that it has different kinetic energy. Generally, the ground is used as the reference frame to study the motion of objects.
- E total = mvs X m0vo
- s = 1 / 2at ^ 2 + v0t
- E increase = E endE0
- E increase
- vt =
- mo Let A be the starting point of the object and B be the end point of the object. vo is the initial velocity A (X1, Y1) B (X1, Y2)
- The kinetic energy of the object is E = VmL <ab>
- Where m is a variable, the value of m due to the constant increase of the object m belongs to [mo, + ]
- Let V0 be unchanged
- L <ab> = v0t = A (X1-Y1) ^ 2 + B (X2-Y2) ^ 2 L keeps increasing
- Kinetic energy when the object is on the earth and is stationary
- E = vTvGm
- vT is the rotation speed of the earth
- vG is the gravitational velocity of the sun
- Second, set the kinetic energy of the object for circular motion
- E = movor ^ 2 for the kinetic energy of the sun's gravity on the earth
- E = movoS
- S is the area of the object
- Three-dimensional kinetic energy
- E = movoVT
- VT is the volume of the object
- The gravitational kinetic energy of the sun on the earth E = VTmovo
- VT = 4R ^ 3/3
Kinetic energy derivation
- We can choose any inertial reference frame to consider kinetic energy. An object was stationary and accelerated after being subjected to a force. The kinetic energy it gets is the work that the total force does on it.
- Where W represents work,
- According to Newton's second law,
- among them
- In Newtonian mechanics, the mass of an object does not change with the rate.
- Where W represents work and t represents time,
- among them
Kinetic energy description
- Kinetic energy is scalar, there is no direction, only magnitude. And it cannot be less than zero. Consistent with work, can be directly added and subtracted.
- Kinetic energy is a relative quantity. The v in the formula is related to the selection of the reference system. In different reference systems, v is different, and the kinetic energy of the object is also different.
- Particles store energy in motion. However, there are significant errors when the speed is close to the speed of light. The special theory of relativity regards kinetic energy as the mass energy that increases when a particle moves, and the revised kinetic energy formula is applicable to any particle below the speed of light. (See "Static Mass", "Static Mass Performance").
- Impulse
- Impulse is the cumulative effect of force on time. The momentum of the force on the object changes the momentum of the object, and the momentum is equal to the change of the momentum of the object.
- During the collision, the interaction time of the object is extremely short, but the force is very large, and the force changes very drastically in this short time, so it is difficult to accurately measure the force and the acceleration of the object; Sometimes the problem does not need to understand the force and speed at each moment, but only the accumulation of force in the action time and the effect it produces. Such problems, although in principle, can be studied using Newton's laws of motion, but are very inconvenient. In order to deal with such problems easily, the concept of impulse needs to be applied.
Kinetic energy theorem
- The work that force does on an object in a process is equal to the change in kinetic energy in the process.
- The resultant external force (the sum of the external forces to which the object is subjected, and the direction and magnitude of the final resultant force of the object can be calculated by the orthogonal method based on the direction and magnitude of the force). The work done on the object is equal to the change in the kinetic energy of the object.
- expression:
- w1 + w2 + w3 + w4 = W = Ek2-Ek1 (k2) (k1) is the subscript
- W = (1/2) × m × Vt ^ 2- (1/2) × m × Vo ^ 2 (where Vt is the final velocity and Vo is the initial velocity.)
- Among them, Ek2 represents the final kinetic energy of the object, and Ek1 represents the initial kinetic energy of the object. W is the change of kinetic energy, also known as the increase of kinetic energy, and also the total work done by the external force on the object.
- The expression of the kinetic energy theorem is a scalar formula. When a positive external force is applied to the object, the kinetic energy of the object is increased by Ek2> Ek1; otherwise, the kinetic energy of the object is decreased by Ek1> Ek2.
- The displacement and kinetic energy in the kinetic energy theorem should be relative to the same frame of reference.
- 1 The object of kinetic energy theorem study is a single object, or an object system that can be regarded as a single object.
- 2 The calculation formula of the kinetic energy theorem is an equation, and generally the ground is used as the reference frame.
- 3 The kinetic energy theorem is suitable for linear motion of objects, and also for curved motion; it is suitable for constant force work and variable force work; force can be segmented or simultaneous, as long as the positive of each force can be found Negative algebra sum is enough. This is the superiority of the kinetic energy theorem.
- The difference and connection between kinetic energy theorem and Newton's second law
- The kinetic energy theorem evolved from Newton's second law, but the physical content reflected by this theorem is very different from Newton's second law. Newton's second law reflects the instantaneous effect of force on an object. It states that As long as there is a force acting on the object at a certain moment, the object will generate acceleration. The magnitude and direction of the acceleration determine how the state of the object will change, and the kinetic energy theorem reflects the spatial accumulation effect of force on the object. It states that force In a certain process, work is performed on an object, and the kinetic energy of the object's movement changes.
- Newton's second law only solves the problem that the force is constant force and the object moves along a straight line, and the kinetic energy theorem can solve both constant force, straight line problems, and variable force and curve problems, as long as it does not involve acceleration and time. Newton's second law is more concise.
- Proposer
- Coriolis was the first to give a precise modern definition of kinetic energy and work. He defined the kinetic energy of an object as one-half of the mass of the object multiplied by the square of its speed, and the work done by an applied force on an object is equal to the force multiplied by the distance it moved to overcome resistance.
- experiment
- What factors are involved in investigating the magnitude of kinetic energy?
- Conjecture: mass (m), speed (v)
- Experimental methods: (1) control variable method, (2) conversion method.
- Observation method: Compare the magnitude of the kinetic energy of the trolley by observing how far the wooden block is pushed by the trolley.
- Experimental process: (1) Control the quality of the cart, and change the speed of the cart on the horizontal plane by changing the cart's different heights on the inclined plane.
- (2) By controlling the car to slide at the same height on the slope, the speeds of different quality cars to the horizontal plane are the same.
- Experimental conclusion: When the mass of the object is the same, the faster the object moves, the greater the kinetic energy.
Kinetic energy definition
- The energy of an object due to its mechanical movement is
- The concept of kinetic energy was first proposed by GW Leibniz; he called it mana and defined it as
Kinetic energy theorem
- According to the kinetic energy theorem, if a moving object is slowed down until it stops, the object will work on the obstacle. The amount of work done is equal to the original kinetic energy of the object. Therefore, it can be said that kinetic energy is the working force of an object due to its movement. For example, a bullet flying at high speed has kinetic energy, so it can penetrate the steel by punching on the steel plate; the hammer hitting the forging has kinetic energy, so it can work on the forging to deform it.
- At angular velocity
- Where I is the moment of inertia of the rigid body to the axis of rotation. When a rigid body makes plane motion, its kinetic energy is:
- Where m is the mass of the rigid body,
- The kinetic energy when a rigid body rotates around a fixed point is:
- Where
- Is the rigid body for the three inertia principal axes passing through the fixed point O
- Moment of inertia, that is, the principal moment of inertia;
- Angular velocity vector
- In the case of a rigid body performing the most general motion, its kinetic energy is: