Transcript 4 Forces and Newton`s Laws of Motion

CHAPTER 4
Forces and Newton's Laws
of Motion
4.5 Newton's Third Law of
Motion
4.5 Newton's Third Law of
Motion
4.5 Newton's Third Law of
Motion
Whenever one body exerts a force on a second body, the
second body exerts an oppositely directed force of equal
magnitude on the first body.
Examples of Newton's 3rd
Law
Example 4
Suppose that the mass of the spacecraft in Figure 4.7 is mS = 11
000 kg and that the mass of the astronaut is mA = 92 kg. In
addition, assume that the astronaut exerts a force of P = +36 N on
the spacecraft. Find the accelerations of the spacecraft and the
astronaut.
Example 4
Suppose that the mass of the spacecraft in Figure 4.7 is mS = 11
000 kg and that the mass of the astronaut is mA = 92 kg. In
addition, assume that the astronaut exerts a force of P = +36 N on
the spacecraft. Find the accelerations of the spacecraft and the
astronaut.
Astronauts use a tether to stay connected to
the space capsule.
Application of Newton's
Third Law
Some rental trailers include an automatic brake-actuating
mechanism.
4.6 Types of Forces:
In nature there are two general types of forces, fundamental and
non-fundamental.
Fundamental forces:
•Gravitational force
•Strong nuclear force
•Weak nuclear force-----|
•Electromagnetic force--!—Electroweak force
Non-fundamental forces:
Pushing, Pulling, Kicking, Grabbing, etc….
These are related to the electromagnetic force.
They arise from the interactions between the
electrically charged particles that comprise
atoms and molecules.
Fundamental Forces
Fundamental
Force
Strong nuclear
Example
Nucleus
Electromagnetic +, - Charges
Particles
Affected
Nuclear
Relative
Strength
1
Charged
10-2
Weak nuclear
Radioactivity Nuclear
10-15
Gravitational
Your weight
10-38
All
Unification of Fundamental Forces
Newton’s Law of Universal
Gravitation
Every body in the universe attracts every other body with
a force that is directly proportional to the product of the
masses of the bodies and inversely proportional to the
square of the distance between the bodies.
Newton’s Law of Universal
Gravitation
Every body in the universe attracts every other body with
a force that is directly proportional to the product of the
masses of the bodies and inversely proportional to the
square of the distance between the bodies.
Universal Gravitational Constant
m1m2
11
F  G 2 ; G  6.67  10 ( SI ).
r
Universal Gravitational Constant
m1m2
11
F  G 2 ; G  6.67  10 ( SI ).
r
The proportionality constant, G is called the universal
gravitational constant. Its value in the SI system of units is,
G = 6.67  10-11N.m2/Kg2.
Universal Gravitational Constant
m1m2
11
F  G 2 ; G  6.67  10 ( SI ).
r
The proportionality constant, G is called the universal
gravitational constant. Its value in the SI system of units is,
G = 6.67  10-11N.m2/Kg2.
The law of gravitation is universal and very fundamental. It
can be used to understand the motions of planets and moons,
determine the surface gravity of planets, and the orbital
motion of artificial satellites around the Earth.
Acceleration Due to Gravity
Acceleration Due to Gravity
Acceleration Due to Gravity
Acceleration Due to Gravity
Calculate g for planet Earth at sea level.
Weight
Weight = Mass x Gravity
W  m g
The weight of an object is the gravitational force that the
planet exerts on the object. The weight always acts
downward, toward the center of the planet.
SI Unit of Weight: : newton (N)
The Hubble Space
Telescope
Example 6
The mass of the Hubble Space Telescope is 11 600 kg.
Determine the weight of the telescope (a) when it was resting
on the earth and (b) as it is in its orbit 598 km above the
earth's surface.
4.8 The Normal Force
The normal force FN is one component of the force that a
surface exerts on an object with which it is in contact,
namely, the component that is perpendicular to the surface.
Normal Force Is Not Always
Equal to the Weight
Elevator Ride
What happens to your weight during an elevator ride?
Apparent Weight
Apparent Weight