Acceleration. Understanding Speed vs. Velocity Speed is simply how fast Velocity is how fast in a direction Speed = distance/time Velocity = displacement/time.
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Slide 1
Acceleration
Slide 2
Understanding Speed vs. Velocity Speed is simply how fast
Velocity is how fast in a direction Speed = distance/time Velocity
= displacement/time
Slide 3
Self check The speedometer of a car moving east reads 100 km/h.
It passes another car moving west at 100 km/h. Do they have same
speed? Velocity? Same speed but different directions so their
velocities are different. During a certain period of time, the
speedometer of a car reads a constant 60 km/h. Does this indicate a
constant speed? Constant velocity? Speed is constant but direction
may not be constant so velocity may or may not be constant.
Slide 4
Velocity speed in a given direction. Velocities in the same
direction: (+) Add + = 2m/s E + 1m/s E = 3m/s E Velocities in
different directions: (-) Subtract + = 2m/s E - 1m/s W = 1m/s E
Examples EscalatorEscalator TreadmillTreadmill
Slide 5
Dont be so negative It is important Velocities have direction
Since we can have many different directions, in physics we usually
use a + and sign Usually this corresponds to the graphing axis (x
and y)
Slide 6
Acceleration Acceleration - the rate of change in velocity. Any
time Velocity (Speed or direction) changes acceleration = v final -
v initial ------------- time We can usually feel Accelerations
Slide 7
Try It! If a rocket blasts off at 200km/s N into space and
after 8 sec. reaches a velocity of 550km/s N. What was the rockets
acceleration after take off? Step 1 acceleration = v final v
initial time Step 2 acceleration = 550km/s 200km/s 8 s Step 3
acceleration = 43.8km/s/s or km/s 2
Slide 8
Deceleration Deceleration a decrease in velocity over time.
Same formula, just different name Deceleration is negative
acceleration.
Slide 9
Try It! If a car traveling at a velocity of 50 m/s and quickly
stops in 3s for a red light, find the deceleration of the car? Step
1 deceleration = v final v initial time Step 2 deceleration = 0m/s
50m/s 3 s Step 3 deceleration = -16.7m/s/s or m/s 2
Slide 10
Accelerating a Car Gas Pedal If acceleration is positive, then
velocity is increasing Brake Pedal If acceleration is negative,
then velocity is decreasing (deceleration) What other way is there
to accelerate your car?
Slide 11
ACCELERATION 1. The slope of a velocity-time graph is
acceleration just as the slope of a displacement-time graph is
velocity. No slope. No acceleration. a. If the graph is linear,
acceleration is uniform or constant and avg. acceleration =
instantaneous acceleration. b. If the graph is a curve. The
acceleration is different at every point, but instantaneous
acceleration on this graph is still the slope at a point on the
curve.
Slide 12
Remember! Acceleration is a Vector This means that it can have
a sign (+ or -). So, a velocity vs time graph with a positive slope
is a (+) acceleration graph and a velocity vs time graph with a
negative slope is a deceleration graph.
Slide 13
Distance-Time Graph Acceleration is indicated by a curve on a
Distance-Time graph. Changing slope = changing velocity Graphing
Acceleration
Slide 14
A Distance vs. Time Graph Acceleration is represented by a
curved line. A Speed vs. Time Graph Acceleration is represented by
a straight diagonal line.
Slide 15
Graphing Accelerated Motion Speed-Time Graph slope = straight
line = flat line = acceleration + = speeds up - = slows down
constant accel. no accel. (constant velocity)
Slide 16
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
Slide 17
Graphing (+) & (-) Acceleration
Slide 18
Why is it + Acceleration?
Slide 19
Why is it () Acceleration?
Slide 20
Why is there no Acceleration?
Slide 21
Graphing the motion of a Ball thrown Upward
Slide 22
Breaking Down the Throw: Acceleration of the Upward Leg
Slide 23
Breaking Down the Throw: Acceleration of the Downward Leg
Slide 24
Position vs Time Graph of Constant Positive (+)
Acceleration
Slide 25
Position vs Time Graph of Constant Positive Negative
(-)Acceleration
Slide 26
Warm-Up What is acceleration? What is the shape of a distance-
time graph for accelerated motion? What is the shape of a
Speed-time graph for accelerated motion? Why are they
different?
Slide 27
Momentum
Slide 28
Momentum is equal to the mass of an object multiplied by its
velocity. How hard it is to stop a moving object All moving objects
have momentum. http://econtent.bucksiu.org/?a=47768&ch=2
Slide 29
Momentum Inertia in Motion Momentum of an object is, (Momentum)
= (Mass) X (Velocity) P = M V or M V = P Examples of objects with a
large momentum are supertanker (large mass) and bullet (large
velocity).
http://econtent.bucksiu.org/?a=47768&s=00:01:40:17&e=00:02:30:26
http://econtent.bucksiu.org/?a=47768&s=00:04:58:00&e=00:06:07:00
Slide 30
Check Yourself A 2 ton car, going 60 m.p.h. hits a 5 ton truck,
going 20 m.p.h.. Which vehicle, the car or the truck, has greater
momentum? The car because (2)x(60) = 120 and (5)x(20) = 100. What
would the cars speed have to be for the momentums to match? Fifty
m.p.h. since (2)x(50) = (5)X(20). Arent you forgetting something?
The direction of velocity. How does that matter? Rear-end crash not
same as a head-on crash. More about this when we do
collisions.
Slide 31
Conservation of Momentum Law of Conservation of Momentum states
that the total momentum of any group of objects remains the same
unless outside forces act on the object.
http://econtent.bucksiu.org/?a=47768&s=00:07:10:28&e=00:08:01:00
Slide 32
Recoil Momentum conservation also explains recoil (MASS) x
(velocity) (mass) x (VELOCITY)
Slide 33
Wrap Up! What is momentum? What is the law of conservation of
momentum? Using the formula for calculating momentum, determine the
units of measurement?