SAAT Physics 2 Section 3-4 (Work, Energy, and Simple Machines & Energy and Conservation of Energy) - تحصيلي

Work

Is not done by an object unless the object is moved with the action of a force

Work definiton as a formula

W = Fdcosθ

If θ = 0 degrees, then

cos0 degrees = 1

Work has dimensions of

Force times length

In the SI system, work has a unit of

Newtons times meters (Nm) or joules (J)

Work is a scalar quantity

Can be positive or negative

Work is positive when

The component of force is in the same direction as the displacement

Work is negative when

The force is in the direction opposite of the displacement

If the net work is positive,

The object speeds up and the work is done on the object

If the net work is negative,

The object slows down and work is done by the object on something else

Kinetic energy

The energy of an object that is due to the object’s motion (W_net = F△x = ma△)

Kinetic energy depends on

Speed and mass

Kinetic energy is a scalar quantity

The SI unit for kinetic energy (and all other forms of energy) is the joule

Kinetic energy formula

KE = ½ mv²

Kinetic energy formula in words

Kinetic energy = ½ x mass x speed²

The net work done on a body equals

Its change in kinetic energy

The net force work done by a net force acting on an object is

Equal to the change in the kinetic energy of the object

Work-kinetic energy formula

W_net = △KE

Work-kinetic energy formula in words

Net work = change in kinetic energy

W_net = ½ mv²_f - ½ mv²_i

To use this formula, you must include all the forces that do work on the object in calculating the net work done

The object’s speed decreases if the net work is negative

Because the final kinetic energy is less than the inital kinetic energy

The work-kinetic energy theorem allows us to think

Of kinetic energy as the work that an object can do while the object changes speed or as the amount of energy stored in the motion of an obejct

Potential energy

Stored energy

An object in motion has kinetic energy

But a system can have other forms of energy

The gravitational potential energy

Energy associated with an object due to the object’s position relative to a gravitational source

Gravitational potential energy formula

PE_g = mgh

Gravitational potential energy formula in words

Gravitational potential energy = mass x free fall acceleration x height

The SI unit for gravitational potential energy

Joule

Gravitational potential energy depends on

Both the height and the free-fall acceleration, neither which is a property of an object

Elastic potential energy depends on

Distance compressed or stretched

Elastic potential energy

Energy stored in any compressed or stretched object, such as a spring or the stretched strings of a tennis racket or guitar

Elastic potential

Energy available for use when a deformed elastic object returns to its original configuration

Elastic potential energy formula

PE_elastic = ½ KX²

Law of conservation of energy

One of the fundamental laws in physics; it directs microscopic motion of individual atoms in a chemical reaction

Law of conservation of energy states that

Energy can neither be created nor destroyed but can only be converted from one form to another

According to the law of conservation,

The total energy of an isolated system remains conserved over time

Mechanical energy

The sum of kinetic energy and all forms of potential energy associated with an object or group of objects

Mechanical energy formula

ME = KE + ΣPE

All energy that is not mechanical energy (nonmechanical)

Chemical, internal, nuclear, electrical

In the absense of friction,

The total mechnical energy remains the same

Conservation and mechanical energy

When the absence of friction results in mechnical energy remaining the same

Conservation of mechanical energy formula

ME_i = ME_f

½ mv²_i + mgh_i = ½ mv²_f mgh_f

Power

The rate at which work is done; a quantity that measures the rate of the work or how the energy is transformed

Power formula

P = W/△t

W= Fd

P = W/△t = F d/△t

Power formula in words

Power = work divided by time interval

SI unit of power

Watts (W), defined to be one joule per second

Horsepower (hp)

Another unit of power (equal to 746 watts)