C. Acceleration
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![Page 1: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/1.jpg)
C. Acceleration• Acceleration
– the rate of change of velocity– change in speed or direction
t
vva if
a: acceleration
vf: final velocity
vi: initial velocity
t: time
a
vf - vi
t
![Page 2: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/2.jpg)
C. Acceleration
• Positive acceleration–“speeding up”
Negative acceleration “slowing down”
![Page 3: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/3.jpg)
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 m
t = 20 s
v = ?
WORK:
v = d ÷ t
v = (100 m) ÷ (20 s)
v = 5 m/s
You skate faster!vd
t
![Page 4: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/4.jpg)
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/s
t = 3 s
vf = 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/s2a
vf - vi
t
![Page 5: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/5.jpg)
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/s
d = 1km = 1000m
t = ?
WORK:
t = d ÷ v
t = (1000 m) ÷ (330 m/s)
t = 3.03 s
vd
t
![Page 6: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/6.jpg)
D. CalculationsD. 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/s
vf = 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 sa
vf - vi
t
![Page 7: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/7.jpg)
E. Graphing Motion
• slope =
• steeper slope =
• straight line =
• flat line =
Distance-Time Graph
A
B
faster speed
constant speed
no motion
speed
![Page 8: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/8.jpg)
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
![Page 9: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/9.jpg)
0
100
200
300
400
0 5 10 15 20
Time (s)
Dis
tan
ce (
m)
Distance-Time Graph
E. Graphing Motion
• Acceleration is indicated by a curve on a Distance-Time graph.
• Changing slope = changing velocity
![Page 10: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/10.jpg)
E. Graphing Motion
• slope =
• straight line =
• flat line =0
1
2
3
0 2 4 6 8 10
Time (s)
Sp
ee
d (
m/s
)
Speed-Time Graph
acceleration +ve = speeds up -ve = slows down
constant accel.
no accel. (constant velocity)
![Page 11: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/11.jpg)
E. Graphing Motion
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
0
1
2
3
0 2 4 6 8 10
Time (s)
Sp
ee
d (
m/s
)
Speed-Time Graph
![Page 12: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/12.jpg)
III. Defining Force Force
Newton’s First Law Friction
![Page 13: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/13.jpg)
A. Force• Force
– a push or pull that one body exerts on another
– What forces are being exerted on the football?
Fkick
Fgrav
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A. Force• Balanced Forces
– forces acting on an object that are opposite in direction and equal in size
–no change in velocity
![Page 15: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/15.jpg)
A. Force• Net Force
–unbalanced forces that are not opposite and equal
–velocity changes (object accelerates)
Ffriction
W
Fpull
Fnet
NN
![Page 16: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/16.jpg)
B. Newton’s First Law
• Newton’s First Law of Motion– An 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.
![Page 17: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/17.jpg)
B. Newton’s First Law• Newton’s First Law of Motion
– “Law of Inertia”
• Inertia– tendency of an object to resist any change
in its motion– increases as mass increases
![Page 18: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/18.jpg)
ConcepTest 1TRUE or FALSE?
The object shown in the diagram must be at rest since there is no net force acting on it.
FALSE! A net force does not cause motion. A net force causes a change in motion, or acceleration.
![Page 19: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/19.jpg)
ConcepTest 2You are a passenger in a car and not wearing your seat belt.
Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door.
Which is the correct analysis of the situation? ...
![Page 20: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/20.jpg)
ConcepTest 21. Before and after the collision, there is a
rightward force pushing you into the door.
2. Starting at the time of collision, the door exerts a leftward force on you.
3. both of the above
4. neither of the above2. Starting at the time of collision, the
door exerts a leftward force on you.
![Page 21: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/21.jpg)
C. Friction
• Friction– force that opposes motion between 2
surfaces–depends on the:
• types of surfaces• force between the surfaces
![Page 22: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/22.jpg)
C. Friction• Friction is greater...
–between rough surfaces–when there’s a greater
force between the surfaces (e.g. more weight)
• Pros and Cons?
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Ch. 3 & 4Motion & Forces
IV. Force & Acceleration Newton’s Second Law
Gravity Air Resistance Calculations
![Page 24: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/24.jpg)
A. Newton’s Second Law
• Newton’s Second Law of Motion–The acceleration of an object is directly
proportional to the net force acting on it and inversely proportional to its mass.
F = ma
![Page 25: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/25.jpg)
A. Newton’s Second Law
F = maF: force (N)m: mass (kg)a: accel (m/s2)
1 N = 1 kg ·m/s2
am
F
a
Fm
![Page 26: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/26.jpg)
B. Gravity• Gravity
– force of attraction between any two objects in the universe
– increases as...• mass increases• distance decreases
![Page 27: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/27.jpg)
B. Gravity• Who experiences more gravity - the
astronaut or the politician?
less distance
more mass
Which exerts more gravity - the Earth or the moon?
![Page 28: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/28.jpg)
B. Gravity• Weight
– the force of gravity on an object
MASSalways the same
(kg)
WEIGHTdepends on gravity
(N)
W = mgW: weight (N)m: mass (kg)g: acceleration due
to gravity (m/s2)
W: weight (N)m: mass (kg)g: acceleration due
to gravity (m/s2)
W: weight (N)m: mass (kg)g: acceleration due
to gravity (m/s2)
![Page 29: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/29.jpg)
B. Gravity• Would you weigh more on Earth or
Jupiter?
greater gravity
greater weight
greater mass
Jupiter because...
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B. Gravity• Accel. due to gravity (g)
In the absence of air resistance, all falling objects have the same acceleration!
On Earth: g = 9.8 m/s2
mW
g
elephant
m
Wg
feather
![Page 31: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/31.jpg)
C. Air Resistance• Air Resistance
–a.k.a. “fluid friction” or “drag”– force that air exerts on a moving
object to oppose its motion –depends on:
• speed• surface area• shape• density of fluid
![Page 32: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/32.jpg)
C. Air Resistance• Terminal Velocity
–maximum velocity reached by a falling object
– reached when… Fgrav = Fair
Fair
Fgrav
no net force no acceleration constant velocity
![Page 33: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/33.jpg)
C. Air Resistance• Terminal Velocity
increasing speed increasing air resistance until…
Fair = FgravAnimation from “Multimedia Physics Studios.”
![Page 34: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/34.jpg)
C. Air Resistance
• Falling with air resistance
Fgrav = Fair
Animation from “Multimedia Physics Studios.”
heavier objects fall faster because they accelerate to higher speeds before reaching terminal velocity
larger Fgrav
need larger Fair
need higher speed
![Page 35: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/35.jpg)
D. CalculationsWhat force would be required to
accelerate a 40 kg mass by 4 m/s2?
GIVEN:
F = ?
m = 40 kg
a = 4 m/s2
WORK:
F = ma
F = (40 kg)(4 m/s2)
F = 160 N
m
F
a
![Page 36: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/36.jpg)
D. CalculationsA 4.0 kg shotput is thrown with 30 N of
force. What is its acceleration?
GIVEN:
m = 4.0 kg
F = 30 N
a = ?
WORK:
a = F ÷ m
a = (30 N) ÷ (4.0 kg)
a = 7.5 m/s2
m
F
a
![Page 37: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/37.jpg)
D. CalculationsMrs. J. weighs 557 N. What is her
mass?
GIVEN:
F(W) = 557 N
m = ?
a(g) = 9.8 m/s2
WORK:
m = F ÷ a
m = (557 N) ÷ (9.8 m/s2)
m = 56.8 kg
m
F
a
![Page 38: C. Acceleration](https://reader035.fdocuments.in/reader035/viewer/2022062517/5681382a550346895d9fd712/html5/thumbnails/38.jpg)
ConcepTest• Is the following statement true or false?
– An astronaut has less mass on the moon since the moon exerts a weaker gravitational force.
False! Mass does not depend on gravity, weight does. The astronaut has less weight on the moon.