Transcript Unit 6

Bell Ringer
1.What is the difference between speed and
velocity?
2.Why would you want to know a tornados
velocity instead of its speed?
Unit 6: Force and Motion.
Speed: The rate at which an object moves;
speed depends on the distance traveled and the
time taken to travel that distance.
Formula:
SI Unit:
Meters / second
Unit 6: Force and Motion.
Other units commonly used to express speed…
Kilometers per hour, feet per second, miles per
hour
Unit 6: Force and Motion.
Let’s Try:
A football field is about
100 m long. If it takes a
person 20 seconds to
run its length, how fast
(what speed) were they
running?
S=d/t
S = 100 m / 20 s
S = 5 m/s
Unit 6: Force and Motion.
Let’s Try:
The pitcher’s mound in
baseball is 85 m from
the plate. The balls
average speed is 21.25
m/s. How long does it
take for a pitch to
reach the plate?
t=d/s
t = 85 m / 21.25 m/s
t=4s
Unit 6: Force and Motion.
Now it’s time for the
ANIMAL RACE
Unit 6: Force and Motion.
If something is not moving, a horizontal line is
drawn on a distance-time graph
Time is increasing to the right, but its
distance does not change. It is STOPPED.
Unit 6: Force and Motion.
Both are CONSTANT SPEEDS.
A steeper gradient = higher speed.
Unit 6: Force and Motion.
Can you describe
what is happening here?
CHANGING SPEED.
For the first part of the journey, the object moved
at a steady (slow) speed.
It then suddenly increased its speed.
Unit 6: Force and Motion.
Can you describe
what is happening here?
CHANGING SPEED
Unit 6: Force and Motion.
Velocity: The speed of an object in a particular
direction.
An airplanes
velocity is 600
km/h
An airplanes
velocity is 600
km/h SOUTH
Unit 6: Force and Motion.
An objects velocity is
constant ONLY if its speed
and direction don’t CHANGE
Unit 6: Force and Motion.
Which of the following are examples of velocity?
a) 25 m/s forward
b) 1,500 km/hr
c) 55 m/h south
d) All of the above
Letters a and c are examples of velocity
Unit 6: Force and Motion.
Resultant Velocity: The combination of two or
more velocities.
Unit 6: Force and Motion.
If you are riding a bus traveling east at 25 m/s. You
stand up and walk down the bus’s aisle at 1 m/s
east. What is your RESULTANT VELOCITY?
25 m/s east + 1 m/s east = 26 m/s east
Unit 6: Force and Motion.
If you are riding a bus traveling east at 25 m/s. You
stand up and walk down the bus’s aisle at 1 m/s
west. What is your RESULTANT VELOCITY?
25 m/s east - 1 m/s west = 24 m/s east
Unit 6: Force and Motion.
When velocities are in the same direction, add them
together.
When velocities are opposite direction, subtract
them. *The resulting direction is from the larger
velocity!
Unit 6: Force and Motion.
Acceleration: the rate at which velocity changes.
Acceleration = final velocity – starting velocity
time it takes to change velocity
Units for
acceleration:
m/s2
Unit 6: Force and Motion.
You are riding your bike down a hill. At point A your velocity
is 5 m/s south. 2 seconds later you pass point B and your
velocity is now 25 m/s. What is your acceleration from point
A to point B?
Acceleration = 25 m/s – 5 m/s
2s
Acceleration = 10 m/s2 south
Unit 6: Force and Motion.
You are coming up to a stop sign and start to press on the
breaks. 5 seconds from the sign, your velocity is 45 m/s
west. Once you reach the sign you have stopped, your
velocity is 0 m/s west. What is your acceleration as you
approach the sign?
Acceleration = 0 m/s – 45 m/s
5s
Acceleration = -9 m/s2 west
Unit 6: Force and Motion.
Can you describe
Acceleration in which
velocity decreases:
NEGATIVE
ACCELERATION
what is happening here?
Acceleration in which
velocity increases:
POSITIVE
ACCELERATION
Unit 6: Force and Motion.
Can you describe
what is happening here?
Velocity stays the same:
NO ACCELERATION
(CONSTANT VELOCITY!)
Unit 6: Force and Motion.
Can you describe
what is happening here?
CHANGING
ACCELERATION