Momentum Impulse Energy Work Power

Momentum, Energy, Work Momentum, Energy, Work and Powerand Power

Section 1Section 1

MomentumMomentum

MomentumMomentum

• Momentum is related to how much force is need to change the movement of an object

• Momentum equals mass times velocity

• Momentum is a vector

p=mv

MomentumMomentum• In collisions or other

encounters, momentum is transferred between objects

• In any encounter, the total momentum of the objects does not change – it is conserved

Law of Conservation of Momentum

Conserving MomentumConserving Momentum

How is momentum conserved when a cannon is fired?

The mass and velocity of the cannon ball must equal the mass and velocity of the cannon

Units for MomentumUnits for Momentum

• mv = kg m / s• The SI unit for momentum is a

kilogram meter per second• Is that the only way to get

momentum?• F = N = kg m / s2

• Ft = kg m / s2 X s = kg m / sFt = Δmv

ImpulseImpulse• Ft is known as inpulse measured in

Newton seconds• In a collision or other interaction

Impulse = change in Momentum• Seatbelts, airbags and crumple

zones increase the time of acceleration in a crash decreasing the force on you making the crash more survivable

J = Ft

Section 2 Section 2

EnergyEnergy


EnergyEnergy

• Energy is the ability to make change

• The total energy of a system is called mechanical energy

• Energy is divided into two types: Kinetic and Potential

Mechanical Energy = KE + PE

Kinetic EnergyKinetic Energy

• Energy in motion

• For objects in motion, the amount of kinetic energy is dependent on its mass and its velocity

• The kinetic energy of something in motion =1/2 mass times velocity squared

KE = ½ mv2

Kinetic EnergyKinetic Energy

• KE = ½ mv2 or = ½ kg(m/s)2

• kg m2/s2 = 1 Joule

• Joule is the SI unit used to measure energy

James Joule 1818 - 1889James Joule 1818 - 1889

Question?Question?

• Does 10 kg moving a 5 m/s have the same energy as 5 kg moving at 10 m/s?

• Remember KE = ½ mv2

NO

Potential EnergyPotential Energy

• Stored energy in a motionless object – has the potential or ability to cause change–Elastic - objects that are

stretched or compressed

–Chemical – chemical bonds

–Gravitational – Height

Potential EnergyPotential Energy

• PE - energy stored in things above the earth

• PE depends on mass, height and acceleration due to gravity

PE = mgh

PEPE

• PE = m X 9.8 m/s2 X height• That’s kg X m/s2 X m or kg m2/s2

• kg m2/s2 = 1 Joule, the same as kinetic energy

• What is the PE of a 10 kg mass 5 m above ground?

• PE = 10 X 5 X 9.8 = 490 J

Law of Conservation of EnergyLaw of Conservation of Energy

• Energy may change from one form to another, but the total amount never changes

• As an example, what happens in a swing?

• If the energy of a swing decreases, some other object must increase its energy by an equal amount

Section 3Section 3

WorkWork


Work - DefinedWork - Defined• Transfer of energy that occurs

when a force makes an object move

• The object must move for work to be done

• The motion of the object must be in the same direction as the applied force

Work is Related to EnergyWork is Related to Energy

• Energy is always transferred from the object doing the work to the object on which the work is done

• Work is done on an object only when a force is being applied to the object and the object moves

Calculating WorkCalculating Work

• Work equals force (in Newtons) times distance

W = F X D

Work UnitsWork Units

• W = FXD

• W = N X m or kg m2/s2

• Kg m2/s2 are the same units as energy

• Therefore work is measured in Joules

Question TimeQuestion Time

If you hold 100 kg over your head, are you doing

any work?

NO!

Section 4Section 4

PowerPower


Work and TimeWork and Time

• The relationship between work and time is called power

• Power equals work / time

P = W / T

Power UnitsPower Units

• P = W/T

• P = Joules/sec

• Joule/sec = Nm/sec = watt (W)

• Since work and energy are related, power also can be calculated by dividing energy by time

James WattJames Watt

Scottish scientist and inventor 1736 - 1819

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Momentum Impulse Energy Work Power