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Physics
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Physics is a science that deals with the behavior of matter and the forces that govern everything in the universe. It extends from the unimaginably small subatomic particles to the vastness of galaxies.
Section Introduction
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In this section you will learn to:
- Define common physics terms and identify their units of measurement
- Match Newton`s Laws of Motion with their definitions
- List several types of energy
- Define kinetic energy, potential energy, and work
- Identify the relationship between energy and work.
Section objectives
Outline: two sections
- Laws of Motion and Energy and Work.
- Provide instruction physics principles and applications.
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 In 1666, our old friend, Isaac Newton, was musing on the motions of heavenly bodies while sitting in a garden in Lincolnshire England, where he had gone to escape the plague then ravaging London.

What if the force of gravity, the same force that causes an apple to fall to the ground in this garden, extends much further than usually thought? What if the force of gravity extends all the way to the moon? Newton began to calculate the consequences of his assumption…
 
Introduction
https://www.youtube.com/watch?v=h48BWDeBLno
Isaac Newton, 1642-1727
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Mass and Force
Force: push or pull
Force is a vector – it has magnitude and direction
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Mass and Force
Force: push or pull
Force is a vector – it has magnitude and direction
Mass is the measure of how hard it is to change an object’s velocity.
Mass can also be thought of as a measure of the quantity of matter in an object.
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Velocity and Acceleration
Velocity is the speed at which an object moves in a specified direction. v (m/s).
Acceleration is the rate of change of the velocity.

Video:https://www.youtube.com/watch?v=4dCrkp8qgLU
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Forces and Torque
Force is the amount of "push" or "pull" that an object experiences when it is being accelerated. A force of 1 N will accelerate a 1 kg object at 1 m/s2. In fact, a Newton is equivalent to a kg·m/s2.

A force that turns an object through an angle is called a torque. Torque is usually abbreviated as t and has units of Newton·meters (N·m).

Video Torque: https://www.youtube.com/watch?v=DPTC1Txa9Wo
Force https://www.youtube.com/watch?v=5Zrphnd_0VI
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Work and Energy
Work measures the amount of effort required to move an object against a resistance. Work is typically abbreviated as W, but you may see other abbreviations. A 1 N force that moves an object 1 m has done 1 J of work.

(where d = distance)

Energy is defined as the capacity to do work.
Energy is abbreviated many different ways depending on the context and the type of energy that is being measured. Energy, like work, is measured in Joules (J).
Video: https://www.youtube.com/watch?v=2WS1sG9fhOk
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Work and Energy
Power is the rate at which work is done. It is usually abbreviated P. The standard unit for power is the Watt (W) which is equivalent to a Joule per second (J/s).

If 1 J of energy is released every second, the system is producing 1 W of power.

Power = Work/time
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Newton’s Laws of Motion
1st Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.

2nd Law – Force equals mass times acceleration.

3rd Law – For every action there is an equal and opposite reaction.
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Newton`s First Law of Motion
An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.
Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless.
These pumpkins will not move unless acted on by an unbalanced force.
Video
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Newton`s First Law of Motion
Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!
Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
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Newton’s Second Law
Force equals mass times acceleration.

F = ma

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Newton’s Second Law
Force = Mass x Acceleration

Force is measured in Newtons

ACCELERATION of GRAVITY(Earth) = 9.8 m/s2

Weight (force) = mass x gravity (Earth)
Video
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Newton’s Second Law
An object may have several forces acting on it; the acceleration is due to the net force:
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Newton’s 3rd Law

For every force, there is an equal and opposite force
every “action” has a “back-reaction”
these are precisely equal and precisely opposite
You can’t push without being pushed back just as hard
in tug-of-war, each side experiences the same force (opposite direction)
when you push on a brick wall, it pushes back on you!
Force on box by floor (normal force)
Force on box by gravity
box
floor
Video
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Newton’s 3rd Law

Some action-reaction pairs:
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Newton’s 3rd Law

Although the forces are the same, the accelerations will not be unless the objects have the same mass.
Contact forces:
The force exerted by one box on the other is different depending on which one you push.
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Weight
The weight of an object on the Earth’s surface is the gravitational force exerted on it by the Earth.
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Weight
Apparent weight:
Your perception of your weight is based on the contact forces between your body and your surroundings.
If your surroundings are accelerating, your apparent weight may be more or less than your actual weight.
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Normal Force

The normal force is the force exerted by a surface on an object.
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Normal Force

The normal force may be equal to, greater than, or less than the weight.
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Quick Quiz

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Question
1. Acceleration is a measure of:
A. Your speed as you travel in a straight line.
B. The force due to gravity
C. The rate of change of the velocity.
D. The amount of inertia in a system.
2. Work is measured in units of:
A. Joules (J)
B. Torque (N.m )
C. Newtons (N)
D. Meters per second squared



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Question
3. Density is a measure of:
A. The quantity of matter in an object
B. How much space an object takes up
C. How much an object weighs
D. Mass per unit volume
4.True or False: Energy and Work are measured in the same units.
True
False



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Question
5. Newton`s First Law implies which of the following principles? Select all answers that apply.
A. A body at rest stays at rest if no force acts on it.
B. A body in motion stays in motion if no force acts on it.
C. A body maintains a constant velocity if no force acts on it.
D. When an object starts to move, there must have been a force acting on it.
E. In order to change directions, an object must have a larger mass than the velocity.
6.True or False: Newton`s Second Law states that work equals force times distance.
True
False



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Energy and work are closely related. You have learned that they have the same units and they are defined in terms of each other.


Energy and work
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Types of energy
Energy comes in many forms.
Kinetic Energy
Kinetic energy is the energy of movement. The formula for calculating kinetic energy is:
K = ½mv2
where m and v are the mass and velocity of the object.




Energy and work
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Potential Energy

Potential energy is "stored" energy that is contained inside the object and can be used to do work.

For an object of mass m experiencing a gravitational acceleration g at a height h above the ground, the potential energy U is
U = mgh




Energy and work
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Quick Quiz
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We noted earlier that energy and work are both expressed in Joules. But to many scientists, the relationship between work and energy is more basic than that-work and energy are the same thing!
That is, energy is just the amount of work that theoretically can be done to an object and work is just the amount of energy that can be added to an object.

Saying that the total energy in a system equals the total work the system can do is an alternate way of expressing the First Law of Thermodynamics


Equivalence of Energy and Work
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As an object does work, it must lose energy. There is no way to do work without expending energy in some form. This is why semiconductor factories have such high electricity bills.

The equipment converts the electrical energy into useful forms of work in order to implant ions, etch films, attach chips to substrates or load packages into carriers. Every operation in the factories is an example of converting energy into work.


Converting Energy to Work
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In the simple brick example, all of the potential energy was converted into kinetic energy and could be used to do work. But in reality, no system is capable of converting 100% of its energy into usable work. Any machine will lose energy to the environment in the form of heat or friction. Because the total energy of any system is conserved, the energy lost to the environment is not converted to work.

- For example, let us assume that a diffusion furnace loses 20% of
its electrical energy to heat or friction losses. That means only 80% of the energy is converted to work inside the furnace. We say that the furnace has an efficiency of 80%.
If you can design a more efficient machine, it will require less
energy to do the same amount of work.

Efficiency of Machines
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Kinetic energy is:
A. Stored energy available for work.
B. The energy of movement
C. Always conserved when objects collide.
D. The energy that runs electrical appliances

Potential energy is:
A. Stored energy available for work.
B. The energy of movement
C. Always conserved when objects collide
D. The energy that runs electrical appliances

Question
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3. Select the true statement(s) about energy and work from the list below
A. Work cannot be converted into energy, but energy can be converted into work
B. Work can be converted into energy and energy can be converted into work.
C. The total energy in a system is the same as the amount of work it is theoretically capable of
doing.
D. Some machines are 100% efficient because they have no loss of energy to heat or friction.
E. In a closed system, the total energy must be conserved.


Question
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In this section you learned to:
- Define common physics terms and identify their units of measurement
- Match Newton`s Laws of Motion with their definitions
- List several types of energy
- Define kinetic energy, potential energy, and work
- Identify the relationship between energy and work

Review
Summary of Chapter
Force: a push or pull
Mass: measures the difficulty in accelerating an object
Newton’s first law: if the net force on an object is zero, its velocity is constant
Inertial frame of reference: one in which the first law holds
Newton’s second law:
Free-body diagram: a sketch showing all the forces on an object
Summary of Chapter
Newton’s third law: If object 1 exerts a force on object 2, then object 2 exerts a force – on object 1.
Contact forces: an action-reaction pair of forces produced by two objects in physical contact
Forces are vectors
Newton’s laws can be applied to each component of the forces independently
Weight: gravitational force exerted by the Earth on an object
Summary of Chapter
On the surface of the Earth, W = mg
Apparent weight: force felt from contact with a floor or scale
Normal force: force exerted perpendicular to a surface by that surface
Normal force may be equal to, lesser than, or greater than the object’s weight