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Domain 5 Teacher Notes – SPS8abcde

I. Motion

A. Newton’s Laws of Motion

1. The Law of Inertia or Newton’s First Law: An

object at rest tends to stay at rest and an object

in motion tends to remain in motion in a

straight-line path unless acted on by an

unbalanced force.

a. Inertia is another word for mass. The more

mass an object has, the greater its tendency

to maintain its current state.

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b. Applications:

i. People are often thrown from automobiles

in wrecks because the car comes to a

sudden stop, but the person has a

tendency to stay in motion.

ii. The ride is much smoother on a cruise ship

than a fishing boat, because the cruise ship

is more massive and is not affected as

much by the waves.

2. Newton’s Second Law: The acceleration of an

object is directly proportional to the applied force

and inversely proportional to its mass.

F=ma F= force

m = mass

a = acceleration

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Sample Problem: What is the force exerted by a

2 kg mass that accelerates at 3 m/sec/sec?

mass=2 kg F=ma

acceleration=3 m/sec/sec F =2 kg x 3 m/sec/sec

F=6 kilogram×meter/sec/sec

Check the SCIENCE FACTS AND FORMULAS sheet

1 newton = 1 kilogram×meter/second/second

So the correct answer is 6 newtons.

3. Newton’s Third Law: For every action there is an

equal and opposite reaction.

a. If object A exerts a force on object B, then

object B exerts an equal force on object A in

the opposite direction.

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b. Consequences: Forces always exist in pairs. It

is impossible for you to push on something

without it pushing back. Newton’s Third law

can be used to explain the motion of rockets

and balloons. As the gases exit the balloon or

rocket, they push it in the opposite direction.

B. Motion depends on the observer’s frame of

Reference.

C. Speed

1. A measure of how fast something is moving

2. The distance traveled in a given amount of time

3. Formula speed = distance

time

4. Sample Problem: A bicyclist rides for 1.5 hours

from Snellville to downtown Atlanta. He travels 21

miles. What is his average speed?

d=21 miles speed=distance

t=1.5 hours time

speed= 21 miles

1.5 hours

Speed = 14 mi/hr

D. Velocity

1. Speed in a particular direction

2. formula: velocity = distance and direction

Time

The formula from the SCIENCE FACTS AND FORMULAS sheet is Velocity (V) = V0 + at, where V0 = Initial Velocity, a = Acceleration, and t = Time

3. Sample Problem: What is the average velocity of

a commercial jet that travels west from New York

to Los Angeles (4800 km) in 6.00 hours?

Velocity = distance

time

= 4800 km

6.00 hours

= 800 km/hr west

E. Acceleration

1. The rate at which velocity changes

2. formula: final velocity-initial velocity

acceleration = time

or acceleration =

from SCIENCE FACTS AND FORMULAS sheet

Acceleration = Change in Velocity/Time Elapsed

3. Acceleration occurs if either of these two

conditions exist.

a. The speed of an object is changing. It can be

increasing or decreasing.

The direction of the movement is changing.

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4. Sample Problem: If a car accelerates from 5 m/s to

15 m/s in 2 seconds, what is the car's average

acceleration?

V = 15 m/s

Vo = 5 m/s a= 15 m/s - 5 m/s

t = 2 sec 2 sec

a= 5

II. Forces

Gravitational

The force of gravity between any two objects increases as the mass of either object increases. The force of gravity decreases as the distance between the objects increases.

The force of gravity experienced by something is also known as its weight. Weight can be calculated multiplying mass by the acceleration of gravity (g).

W=mg

Weight depends on both mass and the acceleration of gravity. Mass depends only on the amount of matter in an object. Mass does not change when the location of an object changes.

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The force and weight are both measured in Newtons.

Mass is measured in kilograms. Acceleration is

measured in m/s/s (m/s2).

3. Free Fall

a. A free-falling object is an object which is falling

under the sole influence of gravity.

b. Free-falling objects do not encounter air

resistance.

c. All free-falling objects (on Earth) accelerate

downwards at a rate of approximately 10 m/s/s

(to be more exact, 9.8 m/s/s). This quantity

known as the acceleration of gravity has a

special symbol to denote it - the symbol g.

The distance traveled by a falling object is

calculated using the formula, d = ½ gt2

d. Sample problem: A rock is dropped from the

top of a cliff and strikes the ground 6.5

seconds later. How high is the cliff in meters?

g=9.8 m/sec2 d = ½ gt2

t = 6.5 sec = ½ (9.8 m/sec2) (6.5 sec)2

= ½ (9.8 m/sec2) (42.25 sec2)

= ½ (414.05 m)

= 207 m

Electromagnetic Forces – Like charges repel each

other, opposite charges attract.

1. As the distance between the charges increase, the

magnitude of the force decreases. The same holds

true for magnets.

2. Magnets will always have a North Pole and a South

Pole. Just like with electrical charges, opposite

poles attract. While it is possible to separate

positive and negative charges, it is impossible

to separate north and south magnetic poles.

3. Electric and Magnetic Field Lines- The lines always

go from positive charges to negative charges and

from north poles to south poles. The closer the

Magnetic field is strongest where the lines are closer together

lines, the stronger the field.

1.List a use for electromagnets.

Lift and move cars in a junk yard

2. How can you make a stronger

electromagnet?

a. More coils of wire around the nail

b. More batteries

Electromagnet

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Work

two conditions must be met for work to occur

the object must move through a distance

a force must act upon the object in the direction the object moves

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SI unit for work is the joule, J. (Newton-meter)

Formula: work = force X distance W=F X d

When an object is lifted to a new location or pushed

up a ramp, the work equals the potential energy

gained.

5. Sample Problem: What work is done if Hernando

uses 88 N of force to pull a table 12 meters?

F = 88N Use the formula W=F X d

d = 12 m from the W=88N X 12 m

SCIENCE FACTS AND FORMULAS sheet W= 1056 N-m or

1056 J

Power

the rate of work

SI unit is the watt, W (joule/second)

formula: power = work/time (work divided by time)

4. Sample Problem: When doing a chin-up, a physics

student lifts her 40-kg body [which has a force (weight) of 400 N] a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?

You must first calculate the work done to lift her body

W = F X d

= (400 N) (0.25 m)

W = 100 J

To calculate power

Power= work

time

Power=100 J

2 sec

Power = 50 Watts

III. Energy

Law of conservation of energy.

Energy can neither be created nor destroyed.

It can be changed into other forms.

Two kinds of energy

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Potential energy is stored energy or energy of position. Examples: Magnetic, gravitational, chemical, elastic, and nuclear

PE = mgh where m= mass

g = acceleration due to gravity

h = height

Kinetic energy is energy of motion or energy in action. Examples: a moving baseball or a roller coaster going downhill

KE = ½ mv2

Forms of energy

mechanical energy

Any object which possesses mechanical energy - whether it be in the form of potential energy or kinetic energy - is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be displaced.

b. Simple machines help us lift, pull, increase

elevation of heavy things, change the direction of

the force, increase the force, split things, fasten

things, and cut things

i. inclined plane - Ramp, stairs

ii. wedge – two inclined planes back to back –

screwdriver, knife, axe

iii. screw – inclined plane wrapped around a

cylinder

iv. pulley – rope revolves around a fixed point;

more pulleys make work easier

v. lever – has a fulcrum – see-saw

vi. wheel and axle – bicycle, car, doorknob,

screwdriver in use

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mechanical advantage-the number of times a machine multiplies an effort force.

Formulas from formula sheet:

Actual Mechanical Advantage:

where FR is Force due to resistance and FE is Force due to effort

IMA= Effort Length

Resistance Length

Sample Problem: In a pulley set-up, an effort force of 50 Newtons lifts a resistance force of 100 Newtons. What is the MA of the pulley system?

IMA= Effort Length

Resistance Length

Think about which formula to use

or

AMA= Fr M.A. = 100N

Fe 50N

M.A = 2

Heat, Temperature and Internal Energy

The temperature of an object is directly proportional to the average kinetic energy of its particles. As temperature goes up, particles move faster.

The Internal Energy of a substance is total of the potential and kinetic energy of all its particles.

Energy moving from one location to another is known as heat. Objects do not contain heat. Instead they contain internal energy.

Chemical energy relates to potential energy stored in the bonds between atoms in a compound.

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