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
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
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