541 powerpoint
Transcript of 541 powerpoint
Motion and ForcesDescribing Motion
•Motion•Speed & Velocity
An object at rest will remain at rest, and an object in motion will continue in motion at a constant velocity unless acted upon by a net force.
Newton’s First Law
Motion
Problem:− Is your desk moving?
We need a reference point...− nonmoving point from which motion is measured
Motion
Motion− Change in position in relation to a reference point.
Reference point
Motion
Relative Motion
If you are sitting in a chair reading this sentence, you are moving. You are not moving relative to your desk or your school building, but you are moving relative to the other planets in the solar system and the Sun.
Motion
• Distance• Distance describes how far an object has
moved. • The SI unit of length or distance is the
meter (m). Longer distances are measured in kilometers (km).
• Shorter distances are measured in centimeters (cm).
Motion
• Displacement is the distance and direction of an object's change in position from a reference point.
• Suppose a runner jogs to the 50-m mark and then turns around and runs back to the 20-m mark.
• The runner travels 50 m in the original direction (north) plus 30 m in the opposite direction (south), so the total distance she ran is 80 m.
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.
Speed & Velocity
Speed− rate of motion − distance traveled per unit time
timedistance
speed
sdt
Calculating Speed
The SI unit for distance is the meter and the SI unit of time is the second (s), so in SI, units of speedSometimes it is more convenient to express speed in other units, such as kilometers per hour (km/h).
Speed & Velocity
Instantaneous Speed− speed at a given instant− Speed odometer reading
Average Speed− the total distance traveled divided by the total time of travel
time totaldistance total
speed avg.
Changing Instantaneous Speed
When something is speeding up or slowing down, its instantaneous speed is changing.If an object is moving with constant speed, the instantaneous speed doesn't change.To determine direction you need to know the velocity
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 It depends on the storm’s direction!storm’s direction!
Speed & Velocity
Velocity− speed in a given direction− can change even when the speed is constant!
Speed an Acceleration Video
Calculations Your neighbor skates at a speed of 4 m/s. You can skate Your neighbor skates at a speed of 4 m/s. You can skate
100 m in 20 s. Who skates faster?100 m in 20 s. Who skates faster?
GIVEN:
d = 100 mt = 20 ss = ?
WORK:s = d ÷ t
s = (100 m) ÷ (20 s)
s = 5 m/s
You skate faster!sdt
Calculations Sound travels 330 m/s. If a lightning bolt strikes the Sound travels 330 m/s. If a lightning bolt strikes the
ground 1 km away from you, how long will it take for ground 1 km away from you, how long will it take for you to hear it?you to hear it?
GIVEN:
s = 330 m/sd = 1km = 1000mt = ?
WORK:t = d ÷ s
t = (1000 m) ÷ (330 m/s)
t = 3.03 s
sdt
Graphing Motion
slope =
steeper slope =
Straight line =
flat line =
Single point = instantaneous instantaneous speedspeed
Distance-Time Graph
A
B
faster speedfaster speed
constant speedconstant speed
no motionno motion
speedspeed
Graphing MotionWho 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
0
100
200
300
400
0 5 10 15 20
Time (s)
Dis
tan
ce (
m)
Distance-Time Graph
Graphing Motion
Acceleration is indicated by a curve on a Distance-Time graph.
Changing slope = changing velocity
Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
Sp
ee
d (
m/s
)
Speed-Time Graph
Specify 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
Speed and Velocity
Check on Learning
A
B
C
D
m/s
s
kg
hr
1 _____is a unit of speed.
A
B
C
D
speed, velocity
rate, speed
rate, velocity
speed, acceleration
2_____ describes how fast something is going, whereas, _____describes how fast something is going and in a certain direction.
A
B
C
D
In/hour
m/s
cm/min
none of the answers
3 The SI unit for speed is _____.
A
B
C
D
24 m
6 m
4 m
none of the answers
4 If a person walked at 2 m/s for 12 s, he/she would travel a distance of___
A
B
C
D
slope
Y-intercept
origin
None of the answers
5 The _____ of a distance versus time graph is speed.
A
B
C
D
36.0 m
2160 m
40.0 m
36.0 miles
6How far would you travel moving at 12 m/s for 3.00 minutes?
A
B
C
D
average speed
velocity
given speed
Instantaneous speed
7 The speed at any instant of time is known as_____
A
B
C
D
3974 mi/hr
3 mi/hr
30 mi/hr
30 m/s
8If a total distance of 750 m is covered in a time interval of 25 s, the average speed is _____?
A
B
C
D
3 hours
1 hour
5 hours
50 hours
9How long would it take to travel 50 km traveling at a speed of 10 km/hr?
A
B
C
D
30 s
30 South
30 m/s
30 m/s, South
10 Which of the following is a measure of velocity?
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