physics lesson 9 newton’s second law of motion – force & acceleration eleanor roosevelt high...
TRANSCRIPT
![Page 1: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/1.jpg)
Physics Lesson 9
Newton’s Second Law of Motion – Force &
AccelerationEleanor Roosevelt High School
Chin-Sung Lin
![Page 2: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/2.jpg)
Newton & His Second Law
![Page 3: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/3.jpg)
Review – Newton’s First Law
Usually called the law of inertia
Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by an unbalanced force exerted upon it
Implies the second law of motion
![Page 4: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/4.jpg)
Unbalanced Force
Unbalanced force means the net force ≠ 0
What will the unbalanced force result in?
F
![Page 5: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/5.jpg)
Newton’s Second Law
Newton’s second law – Force & Acceleration
The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object
![Page 6: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/6.jpg)
Net Force = 0
Zero net force means zero acceleration
No acceleration is the evidence of zero net force
Zero acceleration means
state of rest or
state of constant velocity
![Page 7: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/7.jpg)
Force Causes Acceleration
Acceleration ~ Net force
(Direct Proportion)
a ~ Fnet
F
a
![Page 8: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/8.jpg)
Mass Resists Acceleration
Acceleration ~ 1/mass
(Inverse Proportion)
a ~ 1/m
m
a
![Page 9: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/9.jpg)
Force Causes Acceleration
Acceleration ~ Net force
a ~ Fnet
Acceleration ~ 1/mass
a ~ 1/m
a = Fnet /m or Fnet = m a
![Page 10: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/10.jpg)
F = m a
![Page 11: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/11.jpg)
Example: How much Force?
?
![Page 12: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/12.jpg)
Example: What’s the Acceleration?
![Page 13: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/13.jpg)
Example: What’s the mass?
m = ?
a = 100 m/s2
F = 1000000 N
![Page 14: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/14.jpg)
Weight is Gravitational Force
Fnet = m a
Fg = m g
or
W = m g
![Page 15: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/15.jpg)
Weight, mass and Acceleration
![Page 16: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/16.jpg)
Weight, mass and Acceleration
![Page 17: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/17.jpg)
Weight on Earth & Moon?
Same Mass
![Page 18: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/18.jpg)
Mass on Earth & Moon?
Same Weight
![Page 19: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/19.jpg)
Friction Force
Friction acts on materials that are in contact with each other, and is always acts in direction to oppose motion
![Page 20: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/20.jpg)
When There is No Friction
![Page 21: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/21.jpg)
Coefficient of Friction (m)
Friction mainly due to the irregularities in the two surfaces
The irregularities between surfaces of different materials are described by the coefficients of friction (m)
Friction mainly determined by the surface and the weight of the object
![Page 22: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/22.jpg)
Friction Force (Ff)
Friction force (Ff) can be categorized into two different types: Static and Kinetic
Maximum Static Friction
Kinetic Friction
Maximum Static Friction
Ff
F
![Page 23: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/23.jpg)
Coefficient of Friction (m)
![Page 24: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/24.jpg)
Static Friction Force
As long as an object does not move, the friction force (Ff) must be equal in size and opposite in direction to the applied force (F)
Ff = F
The static frictional force can have any value from zero up to a max. value (maximum static friction force)
Ff
F
Maximum Static Friction
![Page 25: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/25.jpg)
Maximum Static Friction Force
Maximum static friction force is directly proportional to the normal force and the coefficient of static friction (s).
Ff = FN s
Ff
F
Maximum Static Friction
![Page 26: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/26.jpg)
Example: Static Friction Force
If a block is not moving, what’s the friction force?
50 kg
20 N
![Page 27: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/27.jpg)
Example: Static Friction Force
If the coefficient of static friction between a block and the ground is 0.2, (a) what’s the maximum static friction force? (b) Will the block move? (c) What’s the friction force?
50 kg
80 N
![Page 28: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/28.jpg)
Example: Static Friction Force
If a wooden block is resting on a wooden floor, (a) How much force is required to make the block move? (b) Will the block move? (c) What’s the friction force while moving?
50 kg
100 N
![Page 29: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/29.jpg)
Kinetic Friction Force
If the applied force exceeds the maximum static friction force, the object will slide in the direction of the applied force, and the friction force reduces to a constant value called kinetic friction force
The value of the kinetic friction is independent of the speed of the object Ff
F
Kinetic Friction
![Page 30: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/30.jpg)
Kinetic Friction Force
Kinetic friction force is directly proportional to the normal force and the coefficient of kinetic friction (k).
Ff = FN k
Ff
F
Kinetic Friction
![Page 31: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/31.jpg)
Example: Kinetic Friction Force
If a block is moving at constant velocity, what’s the friction force?
50 kg
20 N
![Page 32: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/32.jpg)
Example: Kinetic Friction Force
If a block is moving and coefficient of kinetic friction between the block and the ground is 0.1, (a) what’s the friction force? (b) What’s the acceleration of the block?
50 kg
80 N
![Page 33: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/33.jpg)
Example: Kinetic Friction Force
If a wooden block is sliding on a wooden floor, (a) what’s the friction force? (b) What’s the acceleration of the block?
20 kg
100 N
![Page 34: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/34.jpg)
Example: Kinetic Friction Force
If a 40-kg block is pushed by a force of 100 N and accelerates at 2 m/s2, (a) what’s the friction force? (b) What’s the coefficient of kinetic friction between the block and the ground?
40 kg
100 N
![Page 35: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/35.jpg)
Example: Kinetic Friction Force
If a 40-kg block is sliding down an incline plane of 30o at constant speed, (a) what’s the friction force while sliding? (b) What’s the coefficient of kinetic friction between the block and the ground?
40 kg
30o
![Page 36: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/36.jpg)
Application – Anti-Lock Brake
![Page 37: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/37.jpg)
Air Resistance
Fg
R
![Page 38: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/38.jpg)
Free Falling & Air Resistance
When there is air resistance (R), the acceleration of a free falling object reduced. The acceleration of a falling object is:
a = Fnet/m = (Fg – R)/m = (mg – R)/m = g – R/m
![Page 39: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/39.jpg)
Air Resistance & Terminal Speed
When the air resistance on an object equals the weight of the object, the net force is zero and no further acceleration occurs. Acceleration terminates: the object has reached its terminal speed or terminal velocity.
a = 0 m/s2 = g – R/m g = R/m R = mg
![Page 40: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/40.jpg)
Reduce the Terminal Speed
![Page 41: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/41.jpg)
Force vs. Pressure
![Page 42: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/42.jpg)
Pressure
Pressure (P):
The amount of force per unit of area
Pressure = Force / Area of application
or P = F/A
Unit:
Newtons per square meter, or pascals (Pa).
![Page 43: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/43.jpg)
Example: Pressure 200 kg
200 kg
5 kg
5 kg
2m x 2m x 2m.2m x .2m x .2m
Which one has larger pressure?
![Page 44: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/44.jpg)
Summary
Newton’s second law - Fnet = m a
Force causes acceleration & mass resists acceleration
Weight is gravitational force - Fg = m g
Acceleration of different masses on Earth
Mass and weight on Earth and moon
Friction force and coefficient of friction (m)
Static friction force and kinetic friction force
![Page 45: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/45.jpg)
Summary
Friction force Ff = m FN
Air resistance and terminal speed
Pressure vs. force
![Page 46: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/46.jpg)
Q & A
![Page 47: Physics Lesson 9 Newton’s Second Law of Motion – Force & Acceleration Eleanor Roosevelt High School Chin-Sung Lin](https://reader035.vdocument.in/reader035/viewer/2022062716/56649dfe5503460f94ae66e4/html5/thumbnails/47.jpg)
The End