Motion Chapter 8.1Motion Chapter 8.1Speed

Velocity

Momentum

SpeedDistance traveled divided

by the time during which motion occurred

SpeedSpeedConstant speed means that

an object travels the same distance in the same amount of time

Objects at rest have a speed of 0 m/s

Speed EquationSpeed Equation

Distance

TimeSpeed =

v = dt

Speed ExampleSpeed ExampleSuppose a wheelchair racer

finishes a 132 m race in 18 s. What was the racer’s average speed?

Speed ExampleSpeed Examplespeed = d/tSpeed = 132 meters/18 sSpeed = 7.3 m/s

Are speed and velocity the same?

A car travels at a constant speed of 30 miles/hour. The car makes a left at a speed of 30 miles /hour.

Are speed and velocity the same?

Speed did not change Velocity did change

VelocityVelocityQuantity describing both

speed and directionSame calculation as

speed except that it also designates a direction.

Velocity ExampleVelocity ExampleFind the velocity of a

swimmer who swims exactly 110 m toward the shore in 72 s.

Velocity ExampleVelocity Example V = d/t V = 110 meters/72 seconds Speed = 1.5 m/s Velocity = 1.5 m/s towards the

shore

MomentumMomentumA quantity defined as the

product of an object’s mass and its velocity

The greater the mass or the faster the velocity, the greater the momentum

Momentum EquationMomentum EquationMomentum = mass x

velocityEquation is p=mvp is used to represent

momentum

Momentum ExampleFind the momentum of a

75 kg speed skater moving forward at 16 m/s.

Momentum ExampleMomentum Examplemomentum = mvMomentum = (75 kg)(16m/s)Momentum= 1200 kg • m/s

forward

Conservation of Conservation of MomentumMomentum

The total amount of momentum in a system is conserved

Conservation of Momentum If two vehicles with different

masses are traveling with different velocities and they hit head on, the momentum of the two cars before the collision is the same after the collision.

Acceleration and Force - Chapter 8.2

AccelerationForceFriction and Air-resistanceGravity

AccelerationAcceleration change in velocity divided

by the time in which the change occurred

The greater the acceleration the faster the object is speeding up.

AccelerationAccelerationIf the speed remains

constant, acceleration is zero.SI unit is meter/second per

second (m/s/s or m/s2)

Acceleration Equation

∆ velocity

TimeAcceleration =

a = Vf-vi

Δt

Acceleration ExampleAcceleration ExampleFind the acceleration of a

northbound subway train that slows down from 12 m/s to 9.6 m/s in 0.8 s.

Acceleration Example a = change in v/t Acceleration = (9.6 – 12m/s)/0.8s Acceleration = -3 m/s2 or m/s/s

For constant velocity Zero Acceleration

Accelerating has positive slope

decelerating has a negative slope

ForceThe cause of acceleration

or the change in an object’s velocity

SI unit of force is a newton. (N)

Force

Two Types:

1. Balanced forces do not change motion

Force2. Unbalanced forces result in

a net movement in one direction.

This occurs because the net force on one side is less than the net force on the other.(ex. Tug of War.)

Friction the force between two

objects in contact that opposes the motion of either object

friction maintains balanced forces

Gravity

Gravitational force is determined by the distance between the two masses.

Everything falls at an acceleration of 9.8 m/s2 in the absence of air resistance

Gravity is opposed by air resistance

Gravity Experiments

The Physics of Falling

Horizontal motion has no affect on gravity

Gravity has no affect on horizontal motion.

Gravity only works if you look down. True or False

FALSE

Air ResistanceAir resistance is a form of

frictionAir resistance opposes gravity.Objects with bigger volumes or

smaller densities can experience more air resistance.

Laws of Motion - Chapter 8.3

Newton’s 1st Law

Newton’s 2nd Law

Newton’s 3rd Law

Newton’s 1st LawAn object at rest remains at

rest and an object in motion maintains its velocity unless it experiences an unbalancedunbalanced force.

Inertia

How does this work?

Inertia and a roller coaster

Newton’s 2nd LawThe unbalanced force

acting on an object equals the object’s mass times its acceleration.

F=ma

Measuring ForceForce is measured in

newtons.1 N=1 kg*m/s2

Force ExampleWhat is the force necessary

for a 16000 kg automobile to accelerate forward at 2.0 m/s2?

Force ExampleForce= maForce = (16000 kg)(2.0m/s2)Force = 32000 N

Free Fall the motion of a body when

only the force of gravity is acting on it.

Acceleration of gravity is 9.8m/s2

Everything will fall at this acceleration

Mass vs. WeightMass represents the

measured amount of matter in an object.

Weight is the gravitational force an objects experiences based on its mass.

Mass vs. Weight

Weight = mass x gravityw=mg , weight is a force.

Terminal Velocity

The maximum velocity reached by a falling object.

Terminal VelocityThis occurs when air

resistance is equal to the force due to gravity.

Terminal Velocity of a skydiver is ~200 miles/hr

Newton’s third LawFor every action there is an

equal and opposite reaction Rockets move as a result of

action and reaction.