Motion, Speed, & Velocity

Motion, Speed, & Velocity

What is motion anyway??

• 1. What is meant by saying that motion is relative? For everyday motion, what is motion usually relative to?

Motion

• Motion is a change in position (relative to a reference point)

*reference point- stationary (still) object

Conclusion

Distance vs. Displacement• Distance is the length of the path traveled.• Displacement (from “dis”-place to “dat”-

place) (Brendan Jackson this joke is for you! I know how much you love them!) is the length and direction of a line from start to finish.

• Displacement is a vector quantity that contains both magnitude and direction.

Distance vs. Displacement

• Distance vs. Displacement-path that is traveled -change in position of an object-can be a straight line -must be a straight line-no particular direction -must always indicate directionis needed

Distance and Displacement

• 8km = Distance• 3km NE = Displacement

QUT

City

My PlaceX

3km

River

8 km

N

What is the coach's resulting displacement and distance of travel?

Answer

• The coach covers a distance of• (35 yds + 20 yds + 40 yds) = 95 yards and has a

displacement of 55 yards, left.

Speed• Speed- how fast something moves; must measure 2

quantities 1. distance- traveled by object 2. time- it took to travel that distance• Speed equation S = d t Always remember units! d= meters, kilometers t= sec, min, h s= m/s, m/min, km/hGraphing speed= time on x-axis Distance on y-axis *The slope shows speed

Speed• Speed is a measure of how fast something is

moving.• It is the rate at which a distance is covered• Units of speed could be: km/h, m/s, mi/h, ft/s• In physics we use units of m/s for speed

• s = d/t

s

d

ttime

distancespeed

3 types of Speed

• Instantaneous- rate of motion at any second ex. Speedometer

• Constant- speed that does not vary (most speeds are not constant)• Average- total distance traveled divided by the total

time (good at describing a bike or car trip)

Instantaneous Speed

• Instantaneous speed is speed at any instant in time.

• A speedometer measures speed in ‘real time’ (the instantaneous speed).

Average Speed• Average speed is the average of all

instantaneous speeds; found simply by a total distance/total time ratio

• The average speed of a trip:

timeelapsed

distance total speed average

Motion Graphs- Position-Time Graph

Dis

tan

ce i

n F

eet

Time in Seconds

0 1 2 3 4 5 6 7 8 9

40

120

160

200

80

The Slope is Equivalent to the Average Speed

Distance (ft) Vs. Time (sec.)

Run

RiseSlope

Time

DistanceSpeed

Rise

Run

Motion Graphs – Position vs. Time

constant, rightward (+) velocity of +10 m/s

a rightward (+), changing velocity - that is, a car that is moving rightward but speeding up or accelerating

Slow, Rightward(+)Slow, Rightward(+)Constant VelocityConstant Velocity

Fast, Rightward(+)Fast, Rightward(+)Constant VelocityConstant Velocity

Velocity

• Velocity- describes both speed & direction (east, west, north, south, up, or down) of an object• Velocity can change even when the speed is

constant, simply by changing directions• V = d

t

Velocity Triangle

• Speed and velocity triangles are similar because v = d/t

• Find the equation for displacement, and time using the triangle

• d = v x t• t = d/v

v

d

t

Velocity and Speed• In physics we distinguish between speed and velocity:

• Speed refers to how quickly an object moves (a scalar quantity).

• Velocity is defined as speed in a given direction or rate of change of position (displacement over time). v = x/t

• Velocity refers to both the speed and direction of motion of an object (a vector quantity).

• Motion at constant velocity means that both the speed and direction of an object do not change.

• In a car, we can change the velocity three ways: gas pedal to speed up, brake to slow down or steering wheel to change direction

• What 2 controls on a car enable a change in speed?

• Name another control that enables a change in velocity.