Ch. 18 Motion and Momentum What is motion? Acceleration Momentum.
Ch. 9 Motion
description
Transcript of Ch. 9 Motion
Ch. 9Motion
Describing Motion Motion Speed & Velocity Acceleration
Newton’s First Law
Newton’s First Law of MotionAn object at rest will remain at
rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.
motion
constant velocitynet force
A. MotionProblem:
Is your desk moving?
We need a reference point...nonmoving point from which
motion is measured
A. MotionMotion
Change in position in relation to a reference point.
Reference point
Motion
A. MotionProblem: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 & VelocitySpeed
rate of motion distance traveled per unit time
timedistancespeed
vd
t
B. Speed & VelocityInstantaneous Speed
speed at a given instantAverage Speed
time totaldistance totalspeed avg.
B. Speed & VelocityProblem:
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 & VelocityVelocity
speed in a given directioncan change even when the
speed is constant!
C. AccelerationAcceleration
the rate of change of velocitychange in speed or direction
tvv
a if
a: accelerationvf: final velocity
vi: initial velocity
t: time
avf - vi
t
C. AccelerationPositive acceleration
“speeding up”
Negative acceleration “slowing down”
D. CalculationsYour neighbor skates at a speed of 4 m/s.
You can skate 100 m in 20 s. Who skates faster?
GIVEN:d = 100 mt = 20 sv = ?
WORK:v = d ÷ t
v = (100 m) ÷ (20 s)
v = 5 m/s
You skate faster!vd
t
D. 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:v = 330 m/sd = 1km = 1000mt = ?
WORK:t = d ÷ v
t = (1000 m) ÷ (330 m/s)
t = 3.03 s
vd
t
D. CalculationsA roller coaster starts down a hill at 10 m/s.
Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration?
GIVEN:vi = 10 m/st = 3 svf = 32 m/s
a = ?
WORK:a = (vf - vi) ÷ t
a = (32m/s - 10m/s) ÷ (3s)
a = 22 m/s ÷ 3 s
a = 7.3 m/s2avf - vi
t
D. CalculationsHow long will it take a car traveling 30 m/s
to come to a stop if its acceleration is -3 m/s2?
GIVEN:t = ? vi = 30 m/svf = 0 m/s
a = -3 m/s2
WORK:t = (vf - vi) ÷ a
t = (0m/s-30m/s)÷(-3m/s2)
t = -30 m/s ÷ -3m/s2
t = 10 savf - vi
t
E. Graphing Motion
slope =steeper slope =
straight line =flat line =
Distance-Time Graph
A
B
faster speed
constant speed
no motion
speed
E. 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
0
100
200
300
400
0 5 10 15 20Time (s)
Dis
tanc
e (m
)
Distance-Time Graph
E. Graphing Motion
Acceleration is indicated by a curve on a Distance-Time graph.
Changing slope = changing velocity
E. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
Spee
d (m
/s)
Speed-Time Graph
slope =
straight line =
flat line =
acceleration +ve = speeds up -ve = slows down
constant accel.
no accel. (constant velocity)
E. Graphing Motion
0
1
2
3
0 2 4 6 8 10
Time (s)
Spee
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
VECTOR: Vectors measure using arrows to show direction
and magnitude. Shows direction of the object's motion.
Ex: velocity, acceleration, force. (all involve a direction)
Can you build the perfect paper airplane?
Principles: A glider moves through the air without
the help of a motor or engine. A glider can move through the air and
descend gradually when it is well designed and built.
Think about aerodynamics to build a glider that will fly well. "Drag" "Thrust" "Lift" "Gravity“
Facts: The design of your glider's body and
wings has a lot to do with how well it will sail in the air.
Adding some weight to parts of your glider will help it stay up in the air, have lift, and travel in a straight path instead of spinning or nosediving.