Chapter 10: MotionChapter 10: Motion

Observing Motion Observing Motion Reference point: stationary Reference point: stationary object from which motion object from which motion is observedis observed

Motion involves distance, Motion involves distance, time and directiontime and direction

Displacement measures Displacement measures the change in position or the change in position or the straight-line distance the straight-line distance traveled by an objecttraveled by an object

Measuring MotionMeasuring MotionSpeed: Speed: – how fast an object is movinghow fast an object is moving– distance/time distance/time

Velocity: speed with directionVelocity: speed with directionv= d/tv= d/td=vtd=vtt=d/vt=d/v

Speed can be determined by a Speed can be determined by a distance vs. time graphInstantaneous speed and average speedResultant velocity

Section 2 Section 2 Acceleration

Change in velocityChange in velocity

Can be change in speed orCan be change in speed or

Change in directionChange in direction

Uniform circular motion is constant Uniform circular motion is constant accelerationacceleration

Calculating AccelerationCalculating AccelerationRate at which velocity changes:Rate at which velocity changes:

Acceleration= Acceleration= final velocity – initial vfinal velocity – initial vtimetime

a=a=vvff-v-vii

tt

Units are m/s/s or m/sUnits are m/s/s or m/s22

Related equationsRelated equations

t= t= vvff-v-vii

aa

vvff= at+v= at+vii

vvii= v= vff-at-at

Falling objects: vFalling objects: vff=at=at

GraphsGraphs

Section 3: Motion and ForceSection 3: Motion and Force

A force is a push or a pullA force is a push or a pull

A net force is the combination of A net force is the combination of forces acting on an objectforces acting on an object

Balanced forces produce no net force Balanced forces produce no net force and do not change the motion of an and do not change the motion of an objectobject

Unbalanced forces do not cancel out Unbalanced forces do not cancel out and then cause a change in motionand then cause a change in motion

FrictionFriction

A force that opposes motion between A force that opposes motion between two surfaces that are in contacttwo surfaces that are in contactStatic friction is a stationary force Static friction is a stationary force Kinetic friction opposes the Kinetic friction opposes the movement of two surfacesmovement of two surfaces– Types and examples of kinetic friction:Types and examples of kinetic friction:

RollingRollingSlidingSlidingFluidFluid

Reducing harmful frictionReducing harmful friction

Use of lubricantsUse of lubricants

Replacing sliding friction with rollingReplacing sliding friction with rolling

Make surfaces smootherMake surfaces smoother

Reduce surface areaReduce surface area

Examples: Examples:

Increasing helpful frictionIncreasing helpful friction

Make surfaces rougherMake surfaces rougher

Increase surface areaIncrease surface area

Adding to the forces of the objects in Adding to the forces of the objects in contact (adding weight)contact (adding weight)

Examples:Examples: