MotionMotionChapter 11Chapter 11

Distance and DisplacementDistance and DisplacementTo describe motion accurately and To describe motion accurately and completely a frame of reference is completely a frame of reference is necessary. There can be numerous necessary. There can be numerous frames of reference and it depends on the frames of reference and it depends on the one you choose to measure motion.one you choose to measure motion.Example: One frame of reference on earth- Example: One frame of reference on earth- the sun sets. If you were on the sun the sun sets. If you were on the sun though the earth would be risingthough the earth would be risingRelative motion- movement in relation to a Relative motion- movement in relation to a frame of reference.frame of reference.

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Distance and DisplacementDistance and DisplacementMovement can be Movement can be measured only measured only with reference to with reference to something that is something that is assumed to be in a assumed to be in a fixed place.fixed place.

The most common The most common frame of reference frame of reference is the earthis the earth

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Distance and Displacement cont.Distance and Displacement cont.Distance is the length of a Distance is the length of a path between two points. path between two points. When an object moves in a When an object moves in a straight path distance is the straight path distance is the length between the objects length between the objects starting point and ending starting point and ending pointpoint

The unit is the meterThe unit is the meter

DistanceDistance is a is a scalar quantity which means it has only which means it has only magnitude. Ex. 12 m magnitude. Ex. 12 m

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Distance and Displacement cont.Distance and Displacement cont.

Displacement is the direction Displacement is the direction from the starting point and from the starting point and length of a straight line from length of a straight line from the starting point to the the starting point to the ending point.ending point.

DisplacementDisplacement is a is a vector quantity which means which means it has both magnitude AND it has both magnitude AND direction. Ex. 12 m Northdirection. Ex. 12 m North

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Speed and VelocitySpeed and VelocityMotion – a change Motion – a change of position relative of position relative to a frame of to a frame of reference.reference.

Motion is measured Motion is measured by:by:– 1. distance: length 1. distance: length

between two points between two points in metersin meters

– 2. time measured in 2. time measured in secondsseconds

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Speed and VelocitySpeed and VelocitySpeed is the distance traveled by a moving Speed is the distance traveled by a moving object per unit of timeobject per unit of time

Speed is a Speed is a Scalar: has only magnitudeScalar: has only magnitude

Speed = Speed = distancedistance

timetime

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Speed and VelocitySpeed and Velocity

Problem 1 – What is the speed of a Problem 1 – What is the speed of a jet plane that flies 7200 km in 9 hr.jet plane that flies 7200 km in 9 hr.

Answer – 800 km/hrAnswer – 800 km/hr

Problem 2 – The speed of a cruise Problem 2 – The speed of a cruise ship is 50 km/hr. How far will the ship is 50 km/hr. How far will the ship travel in 14 hours?ship travel in 14 hours?

Answer – 700 kmAnswer – 700 km

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Speed and Velocity cont.Speed and Velocity cont.Velocity is speed in a given Velocity is speed in a given direction. direction.

Velocity is a Velocity is a VectorVectorVelocity = Velocity = displacementdisplacement

time time

Example: A car is Example: A car is traveling 60miles/hr traveling 60miles/hr and moving eastand moving east

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Constant SpeedConstant Speed - does - does not change. When not change. When graphed on a graphed on a distance-time graph distance-time graph constant speed is constant speed is always a straight line.always a straight line.The speed of a moving The speed of a moving object is not always object is not always constant. Dividing constant. Dividing total distance by total total distance by total time gives time gives average average speedspeed..Instantaneous SpeedInstantaneous Speed – – speed at a given speed at a given moment in time moment in time (speedometers, radar (speedometers, radar guns etc.)guns etc.)

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Using GraphsUsing GraphsWhich runner Which runner won the race?won the race?Which runner Which runner stopped for a stopped for a rest?rest?How long did he How long did he stop for?stop for?How long did Bob How long did Bob take to complete take to complete the race?the race?Calculate Albert's Calculate Albert's average speed.average speed.

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AccelerationAccelerationAcceleration- the rate of change in velocityAcceleration- the rate of change in velocityAcceleration = Acceleration = final velocity –initial velocityfinal velocity –initial velocity

change in timechange in time

* units = m/s* units = m/s22 = m/sec/sec = = m/sec/sec = m/sec – m/secm/sec – m/sec

secsec

*Deceleration : a decrease in velocity, or negative *Deceleration : a decrease in velocity, or negative accelerationacceleration

*A curved line on a distance / time graph shows *A curved line on a distance / time graph shows acceleration.acceleration.

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Free FallFree Fall

acceleration of an object toward acceleration of an object toward Earth due to gravityEarth due to gravity

Gravity is 9.80 m/sGravity is 9.80 m/s22 on Earth on Earth

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Using GraphsUsing GraphsWhen is the bus: When is the bus: – decelerating?decelerating?– steady steady

speed?speed?– Stopped?Stopped?

During which part During which part of the journey was of the journey was the bus moving the bus moving fastest?fastest?During which part During which part of the journey did of the journey did the bus have the bus have greatest greatest acceleration?acceleration?Calculate the Calculate the acceleration acceleration between D and E.between D and E.

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Circular MotionCircular MotionAcceleration is a change in velocity. In Acceleration is a change in velocity. In circular motion the velocity is continuously circular motion the velocity is continuously changing because changing because directiondirection continuously continuously changes. An object in circular motion is changes. An object in circular motion is always accelerating even though speed always accelerating even though speed may be constant.may be constant.

Centripetal acceleration – acceleration that Centripetal acceleration – acceleration that is directed toward the center of a circular is directed toward the center of a circular path.path.

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Centripetal AccelerationCentripetal Acceleration

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MomentumMomentumAll moving objects have All moving objects have momentum, abbreviated “p”momentum, abbreviated “p”Momentum is equal to the mass of Momentum is equal to the mass of an object multiplied by its velocity.an object multiplied by its velocity.p = mvp = mvThe law of conservation of momentum The law of conservation of momentum

states that total momentum of any states that total momentum of any group of objects remains the same group of objects remains the same unless outside forces act on the unless outside forces act on the objects.objects.

Ex. The momentum of the base ball bat Ex. The momentum of the base ball bat is transferred to the ball when the ball is transferred to the ball when the ball and the bat meetand the bat meet

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