What is kinetic energy? (article) | Khan Academy
The relationship between work done on a body and its kinetic energy is very nicely Therefore Work done increases when the Average velocity is greater, even. Three variables are of importance in this definition - force, displacement, and the Combining the equations for power and work can lead to a second equation There are two forms of mechanical energy - potential energy and kinetic energy. Learn what kinetic energy means and how it relates to work. There are a couple of interesting things about kinetic energy that we can see from the equation.
The mechanical energy possessed by a system is the sum of the kinetic energy and the potential energy. Positive work is done on a system when the force doing the work acts in the direction of the motion of the object. Negative work is done when the force doing the work opposes the motion of the object. When a positive value for work is substituted into the work-energy equation above, the final amount of energy will be greater than the initial amount of energy; the system is said to have gained mechanical energy.
When a negative value for work is substituted into the work-energy equation above, the final amount of energy will be less than the initial amount of energy; the system is said to have lost mechanical energy.
There are occasions in which the only forces doing work are conservative forces sometimes referred to as internal forces.
Typically, such conservative forces include gravitational forces, elastic or spring forces, electrical forces and magnetic forces. When the only forces doing work are conservative forces, then the Wnc term in the equation above is zero. In such instances, the system is said to have conserved its mechanical energy. The proper approach to work-energy problem involves carefully reading the problem description and substituting values from it into the work-energy equation listed above.
Inferences about certain terms will have to be made based on a conceptual understanding of kinetic and potential energy.
For instance, if the object is initially on the ground, then it can be inferred that the PEi is 0 and that term can be canceled from the work-energy equation. In other instances, the height of the object is the same in the initial state as in the final state, so the PEi and the PEf terms are the same.
As such, they can be mathematically canceled from each side of the equation.
What is kinetic energy?
In other instances, the speed is constant during the motion, so the KEi and KEf terms are the same and can thus be mathematically canceled from each side of the equation. Finally, there are instances in which the KE and or the PE terms are not stated; rather, the mass mspeed vand height h is given. In such instances, the KE and PE terms can be determined using their respective equations.
Make it your habit from the beginning to simply start with the work and energy equation, to cancel terms which are zero or unchanging, to substitute values of energy and work into the equation and to solve for the stated unknown. The formula to find the work done by a particular force on an object is W equals F d cosine theta.
W refers to the work done by the force F. In other words, W is telling you the amount of energy that the force F is giving to the object. F refers to the size of the particular force doing the work. And the theta and cosine theta refers to the angle between the force doing the work and the displacement of the object.Work, Energy, and Power: Crash Course Physics #9
You might be wondering what this cosine theta is doing in here. This cosine theta is in this formula because the only part of the force that does work is the component that lies along the direction of the displacement.
Work and the work-energy principle (video) | Khan Academy
The component of the force that lies perpendicular to the direction of motion doesn't actually do any work. We notice a few things about this formula.
The units for work are Newton's times meters, which we called joules. Joules are the same unit that we measure energy in, which makes sense because work is telling you the amount of joules given to or taken away from an object or a system.
If the value of the work done comes out to be positive for a particular force, it means that that force is trying to give the object energy.
The work done by a force will be positive if that force or a component of that force points in the same direction as the displacement. And if the value of the work done comes out to be negative, it means that that force is trying to take away energy from the object.
The work done by a force will be negative if that force or a component of that force points in the opposite direction as the displacement.
Often you can look at the starting conditions initial speed and height, for instance and the final conditions final speed and heightand not have to worry about what happens in between. The initial and final information can often tell you all you need to know.
Work and energy Whenever a force is applied to an object, causing the object to move, work is done by the force. If a force is applied but the object doesn't move, no work is done; if a force is applied and the object moves a distance d in a direction other than the direction of the force, less work is done than if the object moves a distance d in the direction of the applied force.
The physics definition of "work" is: The unit of work is the unit of energy, the joule J. Work can be either positive or negative: If the force has a component in the direction opposite to the displacement, the force does negative work. If you pick a book off the floor and put it on a table, for example, you're doing positive work on the book, because you supplied an upward force and the book went up.
If you pick the book up and place it gently back on the floor again, though, you're doing negative work, because the book is going down but you're exerting an upward force, acting against gravity. If you move the book at constant speed horizontally, you don't do any work on it, despite the fact that you have to exert an upward force to counter-act gravity. Kinetic energy An object has kinetic energy if it has mass and if it is moving.
It is energy associated with a moving object, in other words. For an object traveling at a speed v and with a mass m, the kinetic energy is given by: The work-energy principle There is a strong connection between work and energy, in a sense that when there is a net force doing work on an object, the object's kinetic energy will change by an amount equal to the work done: