motion 1
TRANSCRIPT
Motion & ForcesMotion & Forces
To describe Motion, we use these main terms:
Motion Speed / Velocity Acceleration
A. MotionA. Motion
Problem: Is your desk moving?
We need a reference point...A nonmoving point from which
motion is measured (you have to have one to measure motion!)
A. MotionA. Motion
MotionChange in position in relation to
a reference point.
Reference point
Motion
A. MotionA. Motion
Problem:You are a passenger in a car
stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward.
You have mistakenly set yourself as the reference point.
B. Speed & VelocityB. Speed & Velocity
Speed Is the rate of motion The distance traveled per unit
time
time
distancespeed
sd
t
B. Speed & VelocityB. Speed & Velocity
Instantaneous Speedspeed at a given instant
Average Speed
time total
distance totalspeed avg.
we tend to use average speed… why?
B. Speed & VelocityB. Speed & Velocity
Problem:A storm is 10 km away and is
moving at a speed of 60 km/h. Should you be worried?
It depends on the storm’s direction!
B. Speed & VelocityB. Speed & Velocity
Velocity is essentially the same thing as
speed, but in a given direction
B. Resultant VelocityB. Resultant Velocity
combining 2 or more velocities together
if 2 velocities are in the same direction, add them together
if 2 velocities are in opposite directions, subtract the smaller velocity from the larger velocity, and use the direction of the larger velocity
B. Resultant VelocityB. Resultant Velocity
Think about a moving sidewalk… If you walk with the sidewalk, you walk faster than when you just ride the sidewalk, which is faster than if you were walking opposite to the moving sidewalk
C. CalculationsC. CalculationsYour neighbor skates at a speed of 4 m/s.
You can skate 100 m in 20 s. Who skates faster?
GIVEN:
d = 100 m
t = 20 s
s = ?
WORK:
s = d ÷ t
s = (100 m) ÷ (20 s)
s = 5 m/s
You skate faster!sd
t
C. CalculationsC. CalculationsSound travels 330 m/s. If a lightning bolt
strikes the ground 1 km away from you, how long will it take for you to hear it?
GIVEN:
s = 330 m/s
d = 1km = 1000m
t = ?
WORK:
t = d ÷ s
t = (1000 m) ÷ (330 m/s)
t = 3.03 s
sd
t
C. CalculationsC. CalculationsYou are traveling at an average speed of
60 miles per hour. In 1.3 hours, how far can you travel?
GIVEN:
s = 60 mph
t = 1.3 hours
d = ?
WORK:
d = s x t
d = (60 mph) x (1.3 hrs.)
d = 78 miles
sd
t
D. Graphing MotionD. Graphing Motion
slope =
steeper slope =
straight line =
flat line =
Distance-Time Graph
A
B
faster speed
constant speed
no motion
speed
D. Graphing MotionD. Graphing Motion
Who started out faster? A (steeper slope)
Who had a constant speed? A
Describe B from 10-20 min. B stopped moving
Find their average speeds. A = (2400m) ÷ (30min)
A = 80 m/min B = (1200m) ÷ (30min)
B = 40 m/min
Distance-Time Graph
A
B
D. Graphing MotionD. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
Sp
ee
d (
m/s
)
Speed-Time GraphLine going down =
slowing downLine going up =
speeding up
Flat (horizontal) line = moving at a constant speed
Speed of zero = not moving
D. Graphing MotionD. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
Sp
ee
d (
m/s
)
Speed-Time GraphSpecify the time period
when the object was... slowing down
5 to 10 seconds speeding up
0 to 3 seconds
moving at a constant speed 3 to 5 seconds
not moving 0 & 10 seconds