P. Sci.P. Sci.Chapter 11Chapter 11

Motion & Motion & ForcesForces

MotionMotionwhen when something something changes changes positionposition

DistanceDistance

How far the How far the object object travelstravels

DisplacementDisplacement

the distance an the distance an object has been object has been moved from one moved from one position to position to anotheranother

ExampleExample

one car travels from one town to one car travels from one town to another that is another that is 20 km 20 km to the east.to the east.

X→→→→→→→→→→→→→→→→→ XX→→→→→→→→→→→→→→→→→ X

20 km20 km

another car travels around a another car travels around a track for track for 20 km 20 km and ends up at and ends up at the starting point.the starting point.

XX

Both cars traveled a Both cars traveled a distancedistance of of 20 km but the first car’s 20 km but the first car’s displacementdisplacement is is 20 km 20 km east east while the second car’s while the second car’s displacementdisplacement is is 0 km0 km because because it ended up where it started it ended up where it started from.from.

SpeedSpeed

How much How much timetime it takes for a it takes for a change in position to occur or change in position to occur or how how fast fast something moves. something moves.

Any change over time is Any change over time is called a called a raterate..

Speed is the Speed is the rate rate of change of change in position or the rate of in position or the rate of motionmotion..

Kinds of Speed Kinds of Speed 1. 1. InstantaneousInstantaneous

SpeedSpeed – the rate – the rate of motion at any of motion at any given instant.given instant. (speedometer)(speedometer)

2. Constant Speed 2. Constant Speed – a speed that does – a speed that does not not varyvary.. (cruise (cruise control)control)

3. Average Speed3. Average Speed – is the total – is the total distance traveled by totaldistance traveled by total time time of travel. (miles per hour)of travel. (miles per hour)

Formula for speed:Formula for speed:

dd

s = ts = t

VelocityVelocity

is both speed and is both speed and directiondirection Like speed, velocity may Like speed, velocity may changechange Unlike speed, the velocity can Unlike speed, the velocity can

change while the speed stays change while the speed stays constantconstant (Because velocity includes (Because velocity includes both speed and direction, if either value both speed and direction, if either value changes, velocity will change )changes, velocity will change )

Formula for velocity:Formula for velocity:

d d (in a certain direction)(in a certain direction)

v = tv = t

Terminal velocityTerminal velocity

the highest the highest velocity that velocity that will be will be reached by a reached by a falling objectfalling object..

MomentumMomentumA train is harder to stop than a car A train is harder to stop than a car

going at the same speed… why?going at the same speed… why?Train has more Train has more massmassMomentum depends on mass Momentum depends on mass

and and velocityvelocity

Momentum EquationMomentum Equation

p= mvp= mvMomentum (p)= mass Momentum (p)= mass (m) x velocity (v)(m) x velocity (v)

SI unit: kg x m/sSI unit: kg x m/s

Law of Conservation of Law of Conservation of MomentumMomentum

The total amount of momentum The total amount of momentum in a system is in a system is conservedconserved..

AccelerationAcceleration the rate of the rate of changechange of velocity. of velocity. Acceleration is both the rate of Acceleration is both the rate of

change in velocity and the change in velocity and the directiondirection of that change. of that change.

So, even if an objects’ speed So, even if an objects’ speed remains constant remains constant accelerationacceleration occurs if the direction changes.occurs if the direction changes.

AccelerationAcceleration (cont.) (cont.)IF:IF:

an object travels in a straight line an object travels in a straight line acceleration is just the rate of change acceleration is just the rate of change of of speedspeed..

the acceleration is in thethe acceleration is in the same same direction direction as the velocity (change of as the velocity (change of direction) then the object direction) then the object speeds up.speeds up.

the acceleration is in the the acceleration is in the opposite opposite direction direction from velocity then the from velocity then the object object slows downslows down..

To calculate average acceleration, divide To calculate average acceleration, divide the change in velocity by the time interval.the change in velocity by the time interval.

vf - vi vf - vi ∆ v∆ v a = t = t a = t = t Where: Where: a = average accelerationa = average acceleration

vf = final velocityvf = final velocityvi = initial (starting) velocity vi = initial (starting) velocity t = timet = time∆ ∆ = a greek symbol for delta = a greek symbol for delta

(change)(change) and it stands for and it stands for “change in”“change in”

∆ ∆ v = change in velocityv = change in velocity

AccelerationAcceleration

The change in velocity over The change in velocity over time.time.

final velocity – initial velocityfinal velocity – initial velocity

acceleration = timeacceleration = time

oror

vvff - v - vii ∆ v∆ v

a = t or a = t a = t or a = t

Acceleration cont.Acceleration cont. If acceleration is If acceleration is smallsmall

– speed change is – speed change is gradualgradual

If acceleration is If acceleration is largelarge – speed change is – speed change is rapidrapid..

Acceleration cont.Acceleration cont.

PositivePositive acceleration = acceleration = object is object is speeding upspeeding up

Negative Negative acceleration = acceleration =

object is object is slowing downslowing down

3-2-1 Summary3-2-1 Summary

List the 3 equations we List the 3 equations we learned today.learned today.

Give the 2 values you must Give the 2 values you must know to determine velocity.know to determine velocity.

Write the Law of Write the Law of Conservation of Momentum.Conservation of Momentum.