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PHYSICS LANDRITO, RFG LIVING LIGHT ACEDMY, INC.LEARNING MODULE 2012

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Motion: a change in position, measured by distance and time.

Frame of reference: the point from which movement is determined.

- To measure movement, some point must be considered as nonmoving.-

Earth is the most common frame of reference

Speed: the distance traveled by a moving object per unit of time.

- Speed = distance / time

Example 1: Find the speed of a ball that rolls 60 meters in 3 seconds.

Example 2: How long will it take a car traveling 60 mph to go 540 miles?

Example 3: How far can a car going 45 mph go in 2 hours?

Average speed: the speed of moving objects is not always constant. It changes from moment to moment.

Average speed finds the median speed over a given time.

- Average speed = total distance / total timeExample: A car travels 35 miles in 1 hour, then travels 115 miles during the next 2 hours. What is its

average speed?

Velocity: speed in a given direction.

- Velocity = distance / time + directionExample: Find the velocity of a car that takes 3 hours to go 180 miles from Frisco to Austin, TX.

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Acceleration: The rate of change in velocity.

- Acceleration = change in velocity / Time- Acceleration = Vfinal Voriginal / Time

A = V/T

- V is read as delta V. In science the Greek letter D (delta), is used torepresent a change in something, in this case a change in velocity.

- Deceleration: A term commonly used to mean a decrease in speed.Example 1: What is the acceleration of a ball rolling down a hill if it goes from 0 mi/h to 20 mi/h in 5 seconds?

Example2: It takes 10 seconds for a ball to roll to a stop from a speed of 30mi/h. What is its accelerationrate?

Force: any push or pull.

- Forces give energy to objects.- Forces cause a change in motion.- Force = mass x acceleration- Force is measured in Newtons (N)- Mass (m) is in kilograms (kg)- Acceleration (a) is in meters/sec/sec,

( abbreviated as m/s/s or as m/sec2)

- Therefore, one Newton of force is equal to 1 kilogram beingaccelerated to 1 meter per second squared.

- In other words, it can make a one-kilogram object accelerate 1 meter per second faster with eachadditional second.

Example1: What is the force exerted on a 1,200 kg car if it accelerates at a rate of 8 m/s

2

?

Example2: A force of 500N is exerted on a 50 kg object. What will its acceleration rate be?

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Example 3: What is the mass of a bicycle if it exerts a force of 800N while it is accelerating at a rate of

20m/s2?

Friction: a force that opposes motion.

Gravity: the force of attraction between all objects in the universe.

- Gravity is the weakest of the known natural forces, only becoming obvious when massive objects like starsand planets are involved.

- Free fall - an object falling under the influence of gravity. Near the surface of the earth all objects areaccelerated by gravity at a rate of 9.8 m/s/s

Weight: the force of gravity on an objects mass

- Weight = mass x acceleration due to gravityWeight on earth = mass x 9.8 m/s2

Example: What is the weight of an 80 kg man on Earth?

Example 2: What is the weight of an 80 kg man on the moon where the gravity is 1.6 m/s2?

Momentum: the product of the mass of an object and its velocity.

- All moving objects have momentum.- Momentum = Mass x Velocity- Since the letter m is already used to represent mass, scientists have

decided to use the letter p to represent momentum.

Example: What is the momentum of a 2,000 kg truck going 50 mph?

Why does it take so much longer for a large truck to stop than a small car?

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Newtons Laws of Motion

1. Newtons First Law of Motion states that every object will remain in a state of rest or travelling with aconstant velocity unless an external force acts on it.

2. Newtons Second Law of Motion states that the rate of change of an objects momentum is directlyproportional to the force which caused it, and takes place in the direction of the force.

3. Newtons Third Law of Motionstates that when body A exerts a force on body B, B exerts a force equalin magnitude (but) opposite in direction (on A).

Applications of Newtons laws of motion: Seat belts / Rocket travel / Ball games

To Show that F = ma is a special case of Newtons Second Law

From Newton II: Force is proportional to the rate of change of momentum

Force rate of change of momentum

F (mv mu)/t

F m(v-u)/t

F ma

F = k (ma)

F = ma

Note:

k = 1 because of how we define the Newton (a force of 1 N gives a mass of 1 kg an acceleration of 1 m s-2)

The Principle of Conservation of Momentum

states that in any collision between two objects, the total momentum before impact equals totalmomentum after impact,provided no external forces act on the system.

In symbols

Note that if the two objects coalesce (stick together) after collision,

there is only one final velocity, and the above equation becomes

Areas where the principle of conservation of momentum applies:

Collisions (ball games) Acceleration of aircraft Jet aircraft

Newtons Law of Gravitationstates that any two point masses in the universe attract each other with a force

that is directly proportional to the product of their masses, and inversely proportional to the square of the

distance between them.

G (known as big G) is a constant: its value is 6.7 x 10 -11 N m2 kg-2(you dont need to know this).

m1u1 + m2u2 = m1v1 + m2v2

m1 u1 + m2 u2 = (m1 + m2)v3

2

21

d

mGmFg

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Gravity and Weight

We know that weight and mass are related by the following formula:

Weight(as we have seen from the chapter on Force) is merely a shorthand way of saying force due to gravity.

Therefore we could re-write W = mg, as Fg = mg {where Fg represents force due to gravity}

But we have just seen above that2

21

d

mGmFg

We can equate both equations to get2

21

d

mGm= mg

Now on the left hand side one of these masses (m1) represents the mass of the Earth (or any other planet).

m2 represents the mass of a second object, while on the right hand side m also represents the mass of this

object.

So cancelling this m on both sides (corresponding to the mass of the object) we get

This lets us calculate acceleration due to gravity (g) at any distance from a given planet.

Work is defined as the product of Force Displacement.

Work = Force x Displacement

The unit of work is the Joule (J).

Energy is the ability to do work.

The amount of energy something has is also the amount of work it can do. Because work is a form of energy it follows that the unit of energy is also the Joule.

Different Forms of Energy

Kinetic Energy is energy an object has due to its motion.

Formula for Kinetic Energy:

Potential Energy is the energy an object has due to its position in a force field.

The formula for Potential Energy:

Any time work is done energy is transferred*

The Principle of Conservation of Energy*

states that energy cannot be created or destroyed but can only be converted from one form toanother.

Loss in Potential Energy = Gain in Kinetic Energy for a freely falling object

The Solar Constant is the average amount of the Suns energy falling normallyon one metre squaredof the

Earths atmosphereper second.

W = F d

EK = mv2 *

EP = mgh

2d

GMg

W = mg

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Collisions: Kinetic Energy and Momentum

When two objects collide, momentum is conserved provided no external forces act on the system.

Kinetic energy however is not conserved.

This is because some of the kinetic energy gets converted to sound and heat energy.

Power is the rate at which work is done.

OrPower is the rate at which energy is converted from one form to another.

The unit of power is the Watt (W).

To Estimate the Power developed by a person running up a

flight of stairs.

1. Time how long it takes to run up a flight of stairs.2. Calculate the work done in going up the stairs.

This will be the same as your potential energy at the top(mgh), where m is your mass.

3. Divide the work by the time taken.A similar approach could be used to calculate the power developed

by a person repeatedly lifting weights.

Percentage Efficiency

No machine is 100% efficient some energy is always lost in the process.This is why we can never have a Perpetual Motion machine.

Formula to calculate how efficient a machine is:

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Electromagnetic spectrum: the entire range of electromagnetic radiation from the shortest gamma

rays to the longest radio waves, in which visible light makes up only a small fraction

Radio Waves Microwaves Infrared

waves

UV rays Visible

light

x-rays Gamma rays

Increasing frequency

Decreasing wavelength

Visible Spectrum: the range of different colors of light determined by wavelength and frequency

Colour Frequency (Hz) Wavelength (nm)

Red Lowest

Highest

Largest

SmallestOrange

Yellow

Green

Blue

Violet

Additive Colour Theory of Light:

white light is composed of different colours (wavelengths) of light 3 primary colours (red,green, and blue)

Subtractive Colour Theory of Light:

coloured matter selectively absorbs different colours (wavelengths) of light; those that areabsorbed are subtracted from the reflected light that is seen by the eye

Sources of light:

Bioluminescence the ability of a plant/animal to produce light Incandescent light produced from an object (metal) that is at a very high temperature Fluorescent light emitted by substances when they are exposed to electromagnetic

radiation

Phosphorescence the ability to store the energy from a source of light & then emit itslowly over a long time

Chemiluminescence light produced from a chemical reaction without a rise in temperature(i.e. glow sticks)

Triboluminescence producing light from frictionRay Model of Light: light is represented as straight lines. Light travels in straight lines until it

strikes something. The behaviour of light then depends on whether the something is transparent

(transmits light freely), transluscent(transmit some light), or opaque(absorbs and reflects light)

Law of Reflection (i = r)

The angle of incidence equals the angle of reflection as measured from the normal

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Types of Images

Virtual image = any image formed by rays that do not actually pass through the location ofthe image (this type of image is formed in plane, convex, and sometimes with concave

mirrors); its upright and always smaller than object

Real image = an image formed by light rays that converge at the location of the image (thistype of image is formed in concave mirrors); its inverted; size depends on objects distancefrom focal point

Curved Mirror Terminology

Focal Point: the point where light rays meet,

or appear to meet

Vertex: the middle point of a curved mirror

Principal Axis: the imaginary line drawn

through the vertex, perpendicular to the

curved mirror

Focal Length: the distance from the vertex

to the focal point

Magnification = image height (hi) OR Magnification = image

distance (di)

Object height (ho)

object distance (do)

Refraction: is the bending of light as it crosses the boundary between two media (i.e. air and water)

Index of refraction of material = speed of light in vacuum OR n = c/v

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Speed of light in medium

Total internal reflectionoccurs when light reflects completely off the wall within a denser medium

rather than passing through into a less dense medium (i.e. fibre optics)

Lenses

Concave lens (diverging lens) refract light rays away from the principal axiscorrects near-

sightedness

Convex lens (converging lens) refract light rays towards the principal axis corrects far-

sightedness

Human Vision

Cornea outer surface of the eye; refracts light rays directly into eye to aid in focus Pupil allows light to pass through

Iris controls the size of the pupil Retina inner lining at the back of the eye (the projection screen)

Technologies that use light telescopes; cameras, microscopes; lasers; phototonics (i.e. solar cells)

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