1. Newton’s Laws 2nd
acceleration of an object is directly proportional to the net force on it and inversely proportional to its mass
(defines the newton)

2. Newton’s second law of Motion
F=ma
Force = mass x acceleration
Mass = kilogram
Acceleration = m/s2
Force = 1 N (Newton)
Force = 1 kg-m/s2

3. Newton’s second law of Motion
A larger force acting on an object causes a greater acceleration
A larger mass requires a greater force than a smaller mass would require to achieve the same acceleration.
Hitting a ball harder causes a greater acceleration
If you hit a ping pong ball and a tennis ball with the same force, would they have the same acceleration?

4. The greater the mass, the greater the force must be for a given acceleration.
the amount of acceleration depends not only on the force but on the mass being pushed.
For a given force, the acceleration produced is inversely proportional to the mass.

5. More Mass, Less Acceleration
The greater the mass of an object, the less it accelerates when acted on by a force.
13-Sep-18
Physics 1 (Garcia) SJSU

7. Newton’s second law of Motion
A net force acting on an object causes the object to accelerate in the direction of the force.
Acceleration is determined by the size of the force and the mass of the object.
F= ma

8. Mass & Acceleration
For a given force, greater mass, smaller the acceleration
implies
Double the Mass
Triple the Mass
Half the Mass
Half the Acceleration
Third of the Acceleration
Double the Acceleration
implies
implies
Acceleration goes as
the inverse of mass.
Mathematically, we write,
Acceleration ~ 1/(Mass).
13-Sep-18
Physics 1 (Garcia) SJSU

9. Demo: Hammer Head
Hammer a nail into a piece of wood placed on top of massive object (gold brick or huge book).
Inertia of massive object keeps it from moving; can place on top of head and not feel it.
13-Sep-18
Physics 1 (Garcia) SJSU

10. Force is a scalar property
depends on 2 things; Size or strength of the force and the Direction of the force.
Vector.
A quantity with size and direction
Scalars
are described by size only

11. Force
You can measure force with a Spring scale.

12. Mass and Weight should not be confused with...
Volume
the quantity of space an object occupies
Density
the quantity mass per unit volume
Mass
the quantity of matter in an object
the measurement of the inertia
measured in kilograms (kg)

13. Mass & Weight Mass: Quantity of matter in an object
Weight: Force of gravity on an object
Mass is a universal property.
Weight depends on gravity
(different on Moon).
Mass is the measure of inertia.
Metric unit for mass is the kilogram.
Metric unit for weight is Newton (since it’s a force)
Weight
Earth
Moon
13-Sep-18
Physics 1 (Garcia) SJSU

14. Mass Vs. Weight mass vs. force
is a measure of the total amount of matter contained within an object.
is a measure of the force of the Earth’s gravity on the mass of the object.

15. In metric units, the unit of force is the newton,
. A 1-kilogram brick weighs about 10 newtons (more precisely, 9.8 N).
 The books offer the same resistance to speeding up or slowing down regardless of whether it’s on Earth, on the Moon, or on any other body attracting it.
You’d have to provide the same amount of force to accelerate a huge truck to a given speed on a level surface on the Moon as on Earth.

16. An anvil in outer may be weightless, but it is not massless.
The astronaut in space finds that it is just as difficult to shake the “weightless” anvil as it would be on Earth.
If the anvil were more massive than the astronaut, which would shake more—the anvil or the astronaut?

17. Newton’s 2nd Law of Motion
F=ma
N = Kg*m/s2
Newton was the first to discover the relationship between—acceleration, force, and mass.
It states; an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.

18. NEWTON'S 2nd LAW OF MOTION

19. Acceleration is directly proportional to force.

20. Demo: Elevator Cable Tension in elevator cable depends on acceleration
5 m/s2 upward
( ½ g upward)
Zero
acceleration
5 m/s2 downward
( ½ g downward)
10 m/s2 downward
(Free fall)
0 N
15 N
10 N
5 N
1 kg
1 kg
1 kg
1 kg
13-Sep-18
Physics 1 (Garcia) SJSU

21. Weight the force upon an object due to gravity W = mg
Weight = Mass  Acceleration of gravity
W = mg
measured in Newtons (N) in the metric system or pounds (lb) in the British system

22. Mass and Weight
On the Moon the gravitational force is only 1/6 as strong as on the Earth.
In space you are “weightless” but not “massless”.
Your mass does not depend on where your are.
(e.g. Earth, Moon, or space).

23. Location Mass Weight Earth 18.4 kg 180 N Moon 18.4 kg 30 N Space

24. The weight of a 10 kg brick is...
A) 98 N
B) 10 kg
C) 9.8 kg
D) 10 N
E) 98 kg

25. Newton’s Cradle

26. How much force is need to accelerate a 70 kg rider and her 200 kg motorcycle at 4 m/s2?
Mass of rider = 70 kg
Mass of motorcycle =200 kg
Acceleration = 4 m/s2
Force = unknown
Equation F=ma

27. Example Questions
How much acceleration does a 747 jumbo jet of mass 30,000kg experience in takeoff when the thrust of all of the engines is 120,000N?
A) 747 N
B) 4 kg
C) 1/4 kg
D) 4 m/s2
E) 30,000 kg times 9.8 m/s2

28. Example Questions The same net force is applied to two blocks.
If the blue one has a smaller mass than the yellow one, which one will have the larger acceleration?
A) Blue
B) Yellow

29. Example Questions The same net force is applied to two blocks.
If the blue one has a smaller mass than the yellow one, which one will have the larger acceleration?

30. Inertia Friction increases with greater force
Friction is in the opposite direction of the force applied
Doesn’t want to change what it is doing
Momentum

31. Friction reduces net force & resulting acceleration

32. Force that opposes the motion between 2 surfaces that are in contact
Friction
Force that opposes the motion between 2 surfaces that are in contact

33. Friction Depends on Life without Friction Couldn’t stand
Clothes wouldn’t stay on
Depends on
kinds of surfaces
Force pressing surfaces together

34. Friction is a result of irregularities in the surfaces of objects.
The force required to overcome friction is called the static friction force.
The force needed to keep a constant speed is called the kinetic friction force.

35. Friction
Origin of friction is molecular interaction between solid surfaces.
Friction is complicated.
Friction depends on support force and on properties of the surface.
Basic properties of friction first established by Leonardo da Vinci.
13-Sep-18
Physics 1 (Garcia) SJSU

36. Friction depends on 3 things:
The friction force depends on whether or not the surfaces are moving.
The friction force depends on the materials of which the surfaces are made of.
The friction force depends on how hard the surfaces are pressed together. This is called the Normal Force and depends on mass and gravity also known as Weight

37. To get it started Static friction is greater than kinetic friction.
Imagine your car broke down and you have to push it. Which takes more force, to get it started rolling or to keep it rolling?
To get it started
Static friction is greater than kinetic friction.

38. How is a car affected by friction?
Types of Friction
Static
Sliding
Rolling
fluid

39. sliding friction is less than static friction
Once tires start to slide, the frictional force is reduced and off you go
While the tire is rolling, its surface does not slide -it is static friction—and therefore greater than sliding friction.

40. static friction and sliding friction
It is very important that you not jam on the brakes in an emergency stop. (the tires lock in place), sliding, providing less friction than if they are made to roll to a stop.

41. Fluid Friction Occurs when moving through Air, water & oil
includes falling through air

42. Fluid friction is called drag.
Friction occurs also in liquids and gases, collectively called fluids (because they flow)
drag in a fluid depends on the nature of the fluid
drag does depend on speed and area of contact.

43. the amount of fluid pushed aside by a boat or airplane depends on the size and the shape of the craft.
A slow-moving boat or airplane encounters less drag than faster boats or airplanes.
wide boats and airplanes must push aside more fluid than narrow crafts
For slow motion through water, drag is proportional to the speed of the object.

44. Air Drag
In air, drag at most speeds is proportional to the square of the speed
So if an airplane doubles its speed it encounters four times as much drag
At very high speed, however, the simple rules break down when the fluid flow becomes erratic and such things as vortices and shock waves develop.

45. Friction between the tire and the ground is nearly the same whether the tire is wide or narrow.
The purpose of the greater contact area is to reduce heating and wear.

46. Check Yourself
1. What net force does a sliding crate experience when you exert a force of 110 N and friction between the crate and the floor is 100 N?
2. A jumbo jet cruises at constant velocity of 1000 km/h when the thrusting force of its engines is a constant 100,000 N. What is the acceleration of the jet? What is the force of air resistance on the jet?

47. Lubricants
reduce friction by keeping the two sliding surfaces apart with a thin layer of fluid.
Friction is no longer rubbing the surfaces but instead rubbing the lubricant.

49. Another way to reduce friction is to roll an object over a surface.
This is called rolling frictional force instead of kinetic frictional force.

50. Friction and Air Resistance
Friction and air resistance are forces opposing motion.
13-Sep-18
Physics 1 (Garcia) SJSU

51. Force between surfaces in relative motion less that static friction
Sliding friction
Force between surfaces in relative motion
less that static friction

52. Friction The force of friction does not depend on speed.
Once an object is sliding, the friction force remains approximately the same.
Unlike the friction between solid surfaces, fluid friction depends on speed.
A very common form of fluid ?(liquid or gas) friction for something moving through air is air resistance, also called air drag.

53. friction does not depend on the area of contact.
If you slide a smaller surface, all you do is concentrate the same weight on a smaller area with the result that the friction is the same.
Stopping distance when brakes are applied is not affected by the number of tires

54. the force of friction does not depend on speed
It may be more when the crate is at rest and on the verge of sliding
Once sliding the friction force remains approximately the same.

55. friction does not depend on the area of contact
Slide the crate on its smallest surface and all you do is concentrate the same weight on a smaller area with the result that the friction is the same
the friction between a truck and the ground is the same
# of tires do not matter
(More tires spreads the load and reduces the pressure and wear per tire).
stopping distance is not affected by the number of tires

57. Coefficients of Friction Equations
Static force=Coefficient of static x Normal Force (Weight)
Fs = us x N
Kinetic Force=Coefficient of kinetic x Normal Force (Weight)
Fk = uk x N

58. A crate made of wood weighs 85 lbs is on a concrete floor.
What force is required to get it moving?
Fs = us x N
us ; Page 176
us = .6
Fs = .6 x 85 = 51

59. Fk = uk x N uk ; Page 176 uk = .4 Fk = .4 x 85 = 34
Same crate is now moving, what force is needed to keep it moving at a constant speed?
Fk = uk x N
uk ; Page 176
uk = .4
Fk = .4 x 85 = 34

60. Three identical blocks are pulled, as shown, on a horizontal frictionless surface. If tension in the rope held by the hand is 30 N, what is the tension in the other ropes?
The tension on the rope between Block 3 and 2 is "T 1“
using F = ma
T1 = m *10/m T1 = 10 N
if the tension between block 2 and 1 is T2 then using F= ma for both the block 3 and 2 T2 = 2m * 10/m T2 = 20 N
Use F = ma to the whole system
if the mass of a block is "m" 30 = 3ma therefore a = 30/3m =10/m

61. If forces are equal but opposite, they are balanced.
If one force is greater than the opposite force, than it is an unbalanced force.

62. What happens when forces aren’t balanced—when net forces do not equal zero.
(Mechanical equilibrium, ΣF = 0, where forces are balanced.)
The net force on a kicked soccer ball, for example, is greater than zero, and the motion of the ball changes abruptly.
Its path through the air is not a straight line but curves downward due to gravity—again, a change in motion

63. the combination of forces acting on an object is the net force
To increase the acceleration of an object, you must increase the net force acting on it.
Doubling the force doubles the acceleration
The object’s acceleration is directly proportional to the net force acting on it.
We write acceleration ∼ net force ( directly proportional to)
It means any change in one is the same amount of change in the other.
      

64. The quantity of space an object occupies. Newton’s second law
Volume
 The quantity of space an object occupies.
Newton’s second law
 The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
Force
 Any influence that can cause an object to be accelerated, measured in newtons (or in pounds, in the British system).
Free fall
 Motion under the influence of gravitational pull only.
Terminal speed
 The speed at which the acceleration of a falling object terminates because air resistance balances its weight. When direction is specified, then we speak of terminal velocity.

65. A large rocks resistance to a change in motion (its mass) is 100 times that of the pebble. The greater force offsets the equally greater mass.

66. The acceleration of free fall is independent of an object’s mass
The ratio of weight (F) to mass (m) is the same for all objects in the same locality; so, their accelerations are the same in the absence of air resistance. The ratio of weight (F) to mass (m) is the same for the large rock and the small feather; similarly, the ratio of circumference (C) to diameter (D) is the same for the large and the small circle.

67. When Acceleration Is g—Free Fall
The greater the mass of an object, the greater the gravitational force of attraction between it and the Earth.
the acceleration of an object depends not only on the force—in this case, the weight—but also on the object’s resistance to motion, its inertia.
inertia is a resistance to acceleration.
use the symbol g, rather a, to denote that acceleration is due to gravity alone.

68. Free Fall Acceleration
Newton’s Second Law explains why all objects fall with same acceleration.
Ratio of weight/mass always the same since weight depends on mass.
Analogy with ratio of circumference / diameter always equals pi (3.1415…).
13-Sep-18
Physics 1 (Garcia) SJSU

69. A 65 kg person stands on a scale, what is the force of gravity on the person?
FG = m x g
g = 9.8 m/s2
FG = 65 kg x 9.8 m/s2
FG = 637 N

70. Wind tunnel