Physics Chapter 5 - Work & Energy
What is work?
A force that causes a displacement of an object does work on that object.
What is gravitational potential energy?
Gravitational potential energy is the energy associated with an object due to the object's position relative to a gravitational source.
How is height measured for the purposes of Gravitational Potential Energy?
Height is measured relative to some zero level. That could be ground level, or some other level as long as it is a point where the gravitational potential energy for the object is zero.
How does work that changes an object's speed affect whether the work is positive or negative?
If the net work is positive, the object speeds up and the net force does work ON the object. If the net work is negative, the object slows down and work is done BY the object ON another object.
What is the formula for kinetic energy?
KE = 1/2 mv² kinetic energy = 1/2 × mass × (speed)²
How is kinetic energy related to an object's speed and mass?
Kinetic energy depends on both an object's speed and its mass. If a bowling ball and a volleyball are traveling at the same speed, the bowling ball has more kinetic energy because it has more mass.
What is kinetic energy?
Kinetic energy is energy associated with an object in motion.
How does a moving hammer on the verge of striking a nail use it's energy upon striking the nail?
Part of the energy is used to drive the nail into the wall, and part goes into warming the hammer and nail upon impact.
What is potential energy?
Potential energy is stored energy. It is present in an object that has the potential to move because of its position relative to some other location. Potential energy depends not only on the properties of an object but also on the object's interaction with its environment.
How is kinetic energy measured?
The basic unit for measuring kinetic energy is the joule (J)
What is the Work-KInetic Energy Theorem
Wnet = ∆KE net work = change in kinetic energy
How do you find the net work done by a constant net force?
Wnet=Fnet d(cosθ) net work = net force × displacement ×cosine of the angle between them
What units are used to measure work?
Work has dimension of force times length. This is measured in newtons times meters (N×m) or joules (J)
How is work related to the direction of the displacement?
Work is done only when components of a force are parallel to a displacement. Only the component of the force that is in the direction of the object's displacement does work. Components of force perpendicular to a displacement do not do work
Definition of Work
Work is equal to the magnitude of the force, F, times the magnitude of the displacement. W=Fd
What determines whether work is done on an object?
Work is not done on an object unless the object is moved because of the action of a force. The application of force alone does not constitute work.
Can work be positive or negative?
Yes. Work is a scalar quantity and can be positive or negative. Work is positive when the component of force is in the same direction as the displacement, like when you lift a box. Work is negative when the force is in the direction opposite the displacement.
friction converts kinetic energy to
non mechanical energy
work kinetic energy theorem
the net work done by the net force acting on an object is equal to the change in kinetic energy of the object
a more powerful motor can
the same work in a shorter time interval
conservation of energy is
total energy is always conserved
