Transcript Motion & Speed

Motion & Speed
Ch. 3
Motion & Speed
• What is motion?
1. Changing one’s position
2. Moving from one place to another
3. You need a reference point to know if a
position has changed.
Motion & Speed
• Example:
– You look out the window and
the mail truck is parked by the
mailbox.
– One minute later you see it
down the block.
– Even though you didn’t see the
motion you know it moved
because it’s position relative to
the mailbox has changed.
Motion & Speed
• Example:
– The earth’s crust is
constantly in motion, but
you can’t see it move.
– We know it moves
because it’s position
changes relative to our
point of reference – the
sun.
Motion & Speed
• Changing Motion
1. Speed – the distance you are going divided by
the time.
D
S=
T
Motion & Speed
Distance
D
S T
(miles, km, m)
Speed
unit of distance
unit of time
m/s, km/hr
Time
(s, min, hr)
Motion & Speed
• Example:
A car is traveling at a speed of 100 m/s.
How far will it get in 35 seconds?
Motion & Speed
2. Average speed –
total distance / total time
-Used when speed varies
Motion & Speed
• Example:
You set out to ride your bike. You start at
0 km/hr and increase to 20 km/hr.
You then slow to 12 km/hr and come to a
stop at a red light.
The light changes and you speed up to
35 km/hr.
It took you a total of 15 minutes to ride
your bike a total distance of 5 km.
What is your average speed?
Motion & Speed
• Example:
Motion & Speed
3. Instantaneous speed – your rate of
motion at any time
-Speed shown by your speedometer