Оцените презентацию от 1 до 5 баллов!
Тип файла:
ppt / pptx (powerpoint)
Всего слайдов:
34 слайда
Для класса:
1,2,3,4,5,6,7,8,9,10,11
Размер файла:
1.02 MB
Просмотров:
90
Скачиваний:
2
Автор:
неизвестен
Слайды и текст к этой презентации:
№1 слайд![Physics Voronkov Vladimir](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img0.jpg)
Содержание слайда: Physics 1
Voronkov Vladimir Vasilyevich
№2 слайд![Lecture Work, energy and](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img1.jpg)
Содержание слайда: Lecture 3
Work, energy and power
Conservation of energy
Linear momentum.
Collisions.
№3 слайд![Work A force acting on an](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img2.jpg)
Содержание слайда: Work
A force acting on an object can do work on the object when the object moves.
№4 слайд![](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img3.jpg)
№5 слайд![Work Units Work is a scalar](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img4.jpg)
Содержание слайда: Work Units
Work is a scalar quantity, and its units are force multiplied by length. Therefore, the SI unit of work is the newton • meter (N • m). This combination of units is used so frequently that it has been given a name of its own: the joule ( J).
№6 слайд![Work done by a varying force](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img5.jpg)
Содержание слайда: Work done by a varying force
№7 слайд![](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img6.jpg)
№8 слайд![Work done by a spring If the](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img7.jpg)
Содержание слайда: Work done by a spring
If the spring is either stretched or compressed a small distance from its unstretched (equilibrium) configuration, it exerts on the block a force that can be expressed as
№9 слайд![](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img8.jpg)
№10 слайд![](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img9.jpg)
№11 слайд![Work of a spring So the work](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img10.jpg)
Содержание слайда: Work of a spring
So the work done by a spring from one arbitrary position to another is:
№12 слайд![Kinetic energy Work is a](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img11.jpg)
Содержание слайда: Kinetic energy
Work is a mechanism for transferring energy into a system. One of the possible outcomes of doing work on a system is that the system changes its speed.
Let’s take a body and a force acting upon it:
Using Newton’s second law, we can substitute for the magnitude of the net force
and then perform the following chain-rule manipulations on the integrand:
№13 слайд![And finally This equation was](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img12.jpg)
Содержание слайда: And finally:
This equation was generated for the specific situation of one-dimensional motion, but it is a general result. It tells us that the work done by the net force on a particle of mass m is equal to the difference between the initial and final values of a quantity
№14 слайд![Work-energy theorem In the](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img13.jpg)
Содержание слайда: Work-energy theorem:
In the case in which work is done on a system and the only change in the system is in its speed, the work done by the net force equals the change in kinetic energy of the system.
This theorem is valid only for the case when there is no friction.
№15 слайд![Conservative and](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img14.jpg)
Содержание слайда: Conservative and Nonconcervative Forces
Forces for which the work is independent of the path are called conservative forces.
Forces for which the work depends on the path are called nonconservative forces
The work done by a conservative force in moving an object along any closed path is zero.
№16 слайд![Examples Conservative Forces](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img15.jpg)
Содержание слайда: Examples
Conservative Forces:
Spring
central forces
Gravity
Electrostatic forces
Nonconcervative Forces:
Various kinds of Friction
№17 слайд![Gravity is a conservative](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img16.jpg)
Содержание слайда: Gravity is a conservative force:
Gravity is a conservative force:
№18 слайд![Friction is a nonconcervative](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img17.jpg)
Содержание слайда: Friction is a nonconcervative force:
№19 слайд![Power Power P is the rate at](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img18.jpg)
Содержание слайда: Power
Power P is the rate at which work is done:
№20 слайд![Potential Energy Potential](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img19.jpg)
Содержание слайда: Potential Energy
Potential energy is the energy possessed by a system by virtue of position or condition.
We call the particular function U for any given conservative force the potential energy for that force.
Remember the minus in the formula above.
№21 слайд![](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img20.jpg)
№22 слайд![Potential Energy of Gravity](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img21.jpg)
Содержание слайда: Potential Energy of Gravity
№23 слайд![Conservation of mechanical](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img22.jpg)
Содержание слайда: Conservation of mechanical energy
E = K + U(x) = ½ mv2 + U(x) is called total mechanical energy
If a system is
isolated (no energy transfer across its boundaries)
having no nonconservative forces within
then the mechanical energy of such a system is constant.
№24 слайд![Linear momentum Let s](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img23.jpg)
Содержание слайда: Linear momentum
Let’s consider two interacting particles:
and their accelerations are:
using definition of acceleration:
masses are constant:
№25 слайд![So the total sum of](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img24.jpg)
Содержание слайда: So the total sum of quantities mv for an isolated system is conserved – independent of time.
This quantity is called linear momentum.
№26 слайд![General form for Newton s](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img25.jpg)
Содержание слайда: General form for Newton’s second law:
It means that the time rate of change of the linear momentum of a particle is equal to the net for force acting on the particle.
The kinetic energy of an object can also be expressed in terms of the momentum:
№27 слайд![The law of linear momentum](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img26.jpg)
Содержание слайда: The law of linear momentum conservation
The sum of the linear momenta of an isolated system of objects is a constant, no matter what forces act between the objects making up the system.
№28 слайд![Impulse-momentum theorem The](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img27.jpg)
Содержание слайда: Impulse-momentum theorem
The impulse of the force F acting on a particle equals the change in the momentum of the particle.
Quantity is called the impulse of the force F.
№29 слайд![Collisions Let s study the](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img28.jpg)
Содержание слайда: Collisions
Let’s study the following types of collisions:
Perfectly elastic collisions:
no mass transfer from one object to another
Kinetic energy conserves (all the kinetic energy before collision goes to the kinetic energy after collision)
Perfectly inelastic collisions: two objects merge into one. Maximum kinetic loss.
№30 слайд![Perfectly elastic collisions](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img29.jpg)
Содержание слайда: Perfectly elastic collisions
We can write momentum and energy conservation equations:
(1)
(2)
(1)=> (3)
(2)=> (4)
(4)/(3): (5)
№31 слайд![Denoting We can obtain from](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img30.jpg)
Содержание слайда: Denoting
We can obtain from (5)
Here Ui and Uf are initial and final relative velocities.
So the last equation says that when the collision is elastic, the relative velocity of the colliding objects changes sign but does not change magnitude.
№32 слайд![Perfectly inelastic collisions](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img31.jpg)
Содержание слайда: Perfectly inelastic collisions
№33 слайд![Energy loss in perfectly](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img32.jpg)
Содержание слайда: Energy loss in perfectly inelastic collisions
№34 слайд![Units in SI Work,EnergyW,EJ N](/documents_6/3d0dcb7fcc7774367ff3750155c73979/img33.jpg)
Содержание слайда: Units in SI
Work,Energy W,E J=N*m=kg*m2/s2
Power P J/s=kg*m2/s3
Linear momentum p kg*m/s