Unit 2
Force & Motion
Ch. 5 Sec. 1
Speed & Velocity
Speed
Motion involves distance, direction, & speed…
• speed - distance traveled divided by time
– standard unit: meters per second (m/s)
s𝑝𝑒𝑒𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
OR
s=
𝑑
𝑡
Speed is often not constant, thus there
is both average speed and
instantaneous speed…
Average Speed
- determined by dividing
total distance by total time
Instantaneous Speed
- the speed at any given
moment
Representing Motion
• distance-time graph distance is plotted on the yaxis (vertical) & time is on
the x-axis (horizontal)
• can be used to compare the
speeds of objects
• the slope or steepness of the
line indicates the speed
(steeper = faster)
• a horizontal line on a
distance-time graph means
speed is zero
Velocity
• velocity - the speed AND direction of an
object
• velocity has the same units as speed (m/s)
BUT it includes direction too
• a change in speed, direction, or both =
change in velocity
Time to Think…
1. A dancer moves 5m toward the left of the stage over
the course of 15s. What is her average velocity for this
time?
2. If you know an object’s velocity, do you know its
speed? Explain.
3. An airplane flies a distance of 650km at an average
speed of 300km/hr. How long was the flight?
4. A bee flies 25m north of the hive, then 10m east, 5m
west, and 10m south. How far north and east of the
hive is it now?
5. You walk forward at 1.5m/s for 8s. Your friend decides
to walk faster and starts out at 2.0m/s for the first 4s.
But then she slows down and walks forward at 1.0m/s
for the next 4s. Make a distance-time graph of your
motion and your friend’s motion. Who walked
farther?