MOTION: Describing and Measuring

Motion

CHAPTER 10

Measuring MotionMotion is described as a change in positionAn object is considered in motion when observed in relation to a REFERENCE POINT.Describe motions with reference terms such as: north, south, east, west, up, down, right, left, etc.

Frame of ReferenceThe object or point from which movement is determinedAny object can appear to be in motion or at rest depending on the frame of reference of the observer.

Motion can only be determined when there is a frame of referenceEarth is the most commonly used frame of reference

Frame of Referenceand Relative Motion

Example: When you are standing on the ground, that is your frame of reference. Anything you see, watch, or measure will be compared to the reference point of the ground.

Relative Motion is based on the person describing the motion based on their frame of reference.

Frame of Reference

Frame of Reference for theSkydiversa. Plane – in motion away from themb. Themselves – not in motionc. The ground – in motion towards them

Frame of reference for 2 girls…Red Dress Girl uses the moving vehicleAs her frame of reference and is notMovingYellow Dress girl uses her frame of Reference as a stationary position to See the other girl in motion.

Example 1:Sitting at your desk, how fast are you moving?– Relative to the ground: ZERO

– Relative to the sun: 2.97 X104 m/s! An observer standing on the sun would say you are moving at 2.97 X104 m/s

Example 2:While sitting at a red light a bus stops in the lane next to you…as you are daydreaming looking at the side of the bus…you all of a sudden feel like you are rolling backwards Then you realize it is the bus moving forwards when you take into account a stationary frame of reference.This is your brain “confused”

Did you know?Motion Sickness is caused by your brain getting two different sets of information about your body’s motion based on its frame of reference, the information from your eyes and the information from your inner earTo help with motion sickness, try to look forward at a point far in the distance and stay focused on that.

Distance vs. DisplacementDistance• Scalar (amount only)• Direction does NOT matter.• The actual path

matters!• The total distance traveled.

• In the Daytona 500, the cars travel a distance of 500 miles.

Displacement• Vector (amount and

direction)• Direction DOES matter!• The path does NOT

matter!• The straight-line distance

(and direction) the object has travelled from its starting point.

• In the Daytona 500, the cars experience zero displacement (they start where they end).

Distance vs. DisplacementWhat is the overall distance traveled in the picture below? What is the overall displacement in the picture below?

START

Leg 1

Leg 3

Leg 2

End

Leg 1 Distance = ______Leg 1 Displacement = _____

Leg 2 Distance = ______Leg 2 Displacement = _____

Leg 3 Distance = ______Leg 3 Displacement = _____

Final Distance = ______Final Displacement = _____

Distance vs. Displacement

Vector DiagramsThe objects motion is represented with an arrow in the direction traveling. The size of the arrow indicates the relative speed of that object.

Practice with Frames of Reference / Distance and

DisplacementPracticeWorksheet as a class fun with mapping … check out Santa’s route to your house!

Speed and Velocity

A little lesson through music

SPEEDSPEED – the rate of change in position or rate of motionINSTANTANEOUS SPEED – Rate of motion at any given instant – (ex: speedometer in a car)

CONSTANT SPEED – A speed that does not vary – (ex: cruise control)

– Usain Bolt races at ESPN video clip– Usain Bolt Olympics

Constant Speed vs. Instantaneous Speed….Let’s graph

CALCULATING SPEEDWhen we calculate speed, we are calculating the average speed traveled.AVERAGE SPEED – a measure of total distance traveled divided by total time of travel

SPEED (v) = DISTANCE (d)TIME (t)

UNITS FOR SPEED ---- m/s

DISTANCE-TIME GRAPHThe distance covered by an object is noted at regular intervals of time.

Measuring SpeedSport Science - John WallSport Science - Lebron JamesSport Science - Ndamukong Suh

VELOCITYVELOCITY – Describes both speed AND direction.Velocity can change even if the speed of the object does not change.Calculating Velocity:– Velocity = Displacement / time – Answers will include direction

Velocity – Time GraphA velocity – time graph can show acceleration.

Distance-Time Graphvs.

Velocity Time GraphShows velocity of object, time.Can calculate Acceleration

Shows Motion, distance traveled, and time.Can calculate speed.

ACCELERATIONACCELERATION – The rate of change of velocity.Acceleration can be a change in speed OR direction

Circular motion is a constant acceleration– Example: blades of a fan

Acceleration…Let’s graph

Constant Velocity = Zero Acceleration

Positive Velocity = Positive Acceleration

CALCULATING ACCELERATION

Divide the change in velocity by the time interval

Acceleration (a) = (final velocity – initial velocity)

time intervala = (vf – vi)

t* Unit for Acceleration: m/s2 (plus

direction)

Acceleration PracticeNatalie accelerates her skateboard along a straight path from 0 m/s to 4.0 m/s in 2.5 seconds. Find her average acceleration.

a = 4.0 m/s – 0 m/s2.5 s

a = 1.6 m/s2 along her path

* Practice: p. 328 # 2-5

Example: Positive Acceleration

Acceleration = (30 m/s – 0 m/s)/10 s a = 3 m/s/sThe car’s acceleration is increasing 3 m/s2

Examples: Negative Acceleration

a = (0m/s – 20 m/s)/10 s a = - 2 m/s/sThe cars acceleration is decreasing at 2 m/s2

MOTION AND FORCEFORCE – A push or a pull one object puts on another.BALANCED FORCE – Forces that are equal in size and opposite in direction.UNBALANCED FORCE (NET FORCE) – Forces that are unequal in size…Cause a change in motion.– Unbalanced forces always change the

velocity of the object.

Balanced vs. Unbalanced Forces

Balanced Force opposite in direction - pulling

Balanced force pushing on each other

Unbalanced forces….showing displacement of the object

Unblalanced Forces – adding up to displace the object in one direction

Forces that Act on Objects1. Normal Force – A support force when one object is in contact with a stable object (ex: Book on a table)2. Tension Force – A force transmitted through a string, rope, or cable3. Gravitational Force – The force of attraction to a very large object in the universe4. Friction Force – The force that opposes motion between two surfaces.

Normal Force vs. Gravity Force

Tension Force

Friction Force

FRICTIONFRICTION – The force that opposes motion between two surfaces that are touching each other.2 TYPES OF FRICTION:– STATIC FRICTION – The friction between

surfaces that are stationary.– KINETIC FRICTION – The friction between

moving surfaces.Kinetic Friction can be SLIDING or ROLLING

Increasing or Decreasing FrictionIncrease Friction by using rough surfaces – EX: Cleaning surfaces with a rough

spongeDecrease Friction by adding a liquid– Ex: Oil, WD40

Gravity and Force

Gravity is a Field ForceAll objects in the universe have a gravitational force. Larger objects exert more force than smaller objects.

Calculating Gravitational ForceGravitational force (weight) of an objects is proportional to its massForce (gravity) = (mass) (gravity)– Acceleration due to Gravity (g) is equal

to 9.8 m/s2

Newton’s Second LawAn unbalanced force acting on an object causes that object to change speed or directionAcceleration = Force / Mass

Action - ReactionEvery action has an equal and opposite reaction.Example: The truck hits the sign therefore the sign hits the truck with an equal force in the opposite direction.