Chapter 5

Motion◦ An objects change in position relative to a

reference point Reference Point: The object that appears to stay in

place Speed

◦ The distance traveled divided by the time interval during which the motion occurred. Average Speed = total distance/total time

Measuring Motion 5.1

Velocity◦ Not to be confused with speed: it is the speed of

an object in a particular direction Example: a man is walking 1 m/s west.

◦ Resulting Velocity: when two or more objects are combined. Example: A bus is traveling 15 m/s east. A man

stands up and walks forward at 1 m/s east. The Resulting Velocity is 16 m/s east.

Acceleration◦ The rate at which velocity changes over time; an

object accelerates if its speed, direction, or both change Positive Acceleration: an increase in velocity. Negative Acceleration (aka: deceleration): a

decrease in velocity◦ Centripetal Acceleration: the acceleration that

occurs in a circular motion Example: Windmills that are a changing directions

Force◦ A push or a pull exerted on an object in order to change

the motion of the object; force has size and direction◦ Newton: The SI Unit for force◦ Net Force: the combination of all of the forces acting on

an object. Example: Bill is pushing a box with 25 N and Sally is pulling

the box with 30 N. Their Net Force is 55 N, in the direction they are traveling.

◦ Balanced Force: When the forces of an object produce a Net Force of 0 N. Unbalanced Force: when the Net Force does not equal

zero.

What is Force 5.2

Friction◦ A force that opposes motion between two surfaces

that are connect. Example: A book sliding across the table.

◦ Kinetic Friction: the friction between moving surfaces Kinetic mean moving: Like my watch…

◦ Static Friction: You observe static friction when you push an object and it does not move (large furniture). Static means not moving: Static Electricity

◦ Lubricants: substances that are applied to surfaces to reduce friction. Example: Oil for an Engine

Friction: A Force That Opposes Motion 5.3

Gravity◦ A force of attraction between objects that is due

to their masses The Law of Universal Gravitation

◦ Part 1: Gravitational force increases as mass increase. Vice Versa

◦ Part 2: Gravitational forces decrease as distance increases. Vice Versa

Gravity: A Force of Attraction

Weight◦ A measure of the gravitational force exerted on an

object; its value can change with the location of the object

Mass◦ A measure of the amount of matter in an object;

its value does not change.

Chapter 6

Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects.◦ The rate at which objects accelerate to Earth is

9.8m/s/s So, for every second that an object falls, the objects

downward velocity increases by 9.8m/s.

Gravity and Motion 6.1

Calculating the change of velocity of a falling object can be written like this:◦ v = g X t

means change Terminal Velocity

◦ The constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity. Air Resistance: is the force that opposes the motion

of objects through air

Free Fall◦ The motion of a body when only the force of gravity is

acting on the body Orbiting objects are in free fall

Centripetal Force◦ The unbalances force that causes objects to move in a

circular path Centripetal mean “toward the center”

Projectile Motion◦ The curved path that an object follows when thrown,

launched, or otherwise projected near the surface of Earth Angry Birds

Newton’s First Law of Motion◦ An object at rest remains at rest, and an object in

motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

◦ What are some of the reasons we can see the affects of the second part of Newton’s First Law here on Earth? Examples…

Newton’s Laws of Motion 6.2

Inertia◦ The tendency of an object to resist being moved

or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object. Example: Because of inertia you slide toward the

side of a car when the driver turns a corner Draw Example

The acceleration of an object depends on the mass of the object and the amount of force applied.◦ Part 1: Acceleration depends on Mass

The acceleration of an object decreases as its mass increases and that its acceleration increases as its mass decreases.

◦ Part 2: Acceleration depends on Force An object’s acceleration increases as the force on the

object increases, vice versa

Newton’s Second Law

An apple with a mass of 0.102 kg with a Force of 1N will fall at the same rate as a watermelon with a mass of 1.02 kg with a force of 10 N.◦ A = f/m or F = mXa◦

Math and Newton’s Second Law

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first◦ All forces act in pairs – action and reaction

Example: shuttle blasting off, rabbit jumping, baseball hitting a bat

Newton’s Third Law of Motion

Momentum◦ A quantity defined as the product of the mass and

velocity of an object.◦ Example:

Imagine a compact car and a large truck traveling with the same velocity (speed + direction). The drivers of both vehicles put on the brakes at the same time. Which vehicle will stop first Answer:

Section 6.3 Momentum

Calculating Momentum◦ Momentum is expressed as “p”

P = m X v◦ Example

What is the momentum of an ostrich with a mass of 120 kg that runs with a velocity of 16 m/s north? Answer:

Law of Conservation of Momentum◦ The law states that any time objects collide, the

total amount of momentum stays the same. This is true for any collision if no other forces act on the colliding objects. This law applies whether the objects stick together or bounce off each other. Example of “stick together” – football players

tackling each other Example of “bounce off each other” – bowling ball

hitting pins.

Conservation of Momentum and Newton’s Third Law◦ Explain in your own words:

Chapter 8

Work: the transfer of energy to an object by using a force that causes the object to move in the direction of the force◦ Transfer of energy – kinetic energy

One object moves another object◦ Difference between work and force

With force, you can push hard on an object, but it doesn’t move.

An object must move for there to be work done.

Chapter 8.1

Work or No work◦ Pushing a box in the direction you are walking________________◦ Carrying a backpack forward________________◦ Lifting groceries up________________◦ Carrying the groceries to the counter________________

8.1

Calculating Work◦ W=F X d

F: Force, measured in Newton’s (N) D: distance, measured in meters (m) W: work, measured in Joules (J)

◦ Example W=30N X 5m = 150J W=30N X 10m = 300J

Notice that the further the distance the more work is done

8.1

Power: the rate at which work is done or energy is transformed◦ Example: You can sand a piece of wood by hand,

or by using an electric sander. The electric sander is faster, so it uses more power

8.1

Calculating Power◦ P=W/t

P: power, measured using Watts W: Watts, Measured in J/s t: time, Measured in seconds

◦ Example:◦ It takes you 10s to do 150J of work on a box to

move it up a ramp, what is your power output? Answer: ___________ W

Notice the “s” in the Watts is cancelled out by the time, so you do not include it in the answer

8.1

Machine: a device that helps do work by either overcoming a force or changing the direction of the applied force.

Work Input: the work done on a machine; the product of the input force and the distance through which the force is exerted.◦ How much force you put into it, in a direction

Work Output: the work done by a machine; the product of the output force and the distance through which the force is exerted.◦ The amount work done by the machine

8.2 What is a machine?

Force-Distance Trade-Off◦ If you pick a box straight up, 1 meter with 450 N

of force, the outcome is 450 J. (450N X 1m)◦ If you use a ramp that is 3 meters long, it only

takes you 150 N of force to move the box, the outcome is still 450 J. (150N X 3m) Notice when you use a machine, a ramp, it uses less

force to move the box, but the same results occur.

8.2

Mechanical Advantage: a number that tells how many times a machine multiplies force.\◦ Examples:

Pulley helps lift objects up Levers help pry things apart

◦ Calculating Mechanical Advantage MA=output force/input force

Example: MA=500N/50N = 10 There is no unit. You said say the machine multiplies its

force by 10.

8.2

Mechanical Efficiency: a quantity, usually expressed as a percentage, that measures the ratio of work output to work input◦ Calculating Mechanical Efficiency

ME = work output/work input X 100 The unit is percent, %

◦ Machine can never be 100% efficient, because every machine has some work input, which causes friction, therefor using some energy.

8.2

Lever: a simple machine that consists of a bar that pivots at a fixed point called a fulcrum◦ First Class Lever: The fulcrum is between the input

force and the load, always change the direction of the input force. Ex: push down = load goes up

◦ Second Class Lever: The load is between the fulcrum and the input force, the direction of the input force and load are the same. Ex: push up = goes up

◦ Third Class Lever: The input force is between the fulcrum and the load, the diction of the load and input are the same. Ex: a hammer

8.3 Types of Machines

Pulley: a simple machine that consists of a wheel over which a rope passes over

8.3

Wheel and Axel: a simple machine consisting of two circular objects of different sizes; the wheel is the larger of the two objects

8.3

Inclined Planes: a simple machine that is a straight, slanted surface, which facilitates the raising of loads; a ramp.

Wedge: a simple machine that is made up of two inclined planes and that moves; a knife

Screw: a simple machine that consists of an inclined plane wrapped around a cylinder

8.3

Compound Machine: a machine made of more than one simple machine

8.3

Chapter 17

17.1 Electric Charge and Static Electricity

Law of Electric Charges: States that like charges repel, or push away, and opposite charges attract

Electric Force: the force of attraction or repulsion on a charged particle that is due to an electric field

Electric Field: the space around a charge object in which another charged object experiences an electric field

17.1

Ways to Charge an Object◦ Friction: happens when electrons are “wiped”

from one object onto another◦ Conduction: happens when electrons move from

one object to another by direct contact◦ Induction: happens when charges in an

uncharged metal

17.1

Electrical Conductors: is a material in which charges can move freely◦ Examples:

Electrical Insulator: a material in which charges cannot move freely◦ Examples:

Static electricity: electric charge at rest; generally produced by friction or induction

Electric Discharge: the release of electricity stored in a source - lightning

17.1

Electric Current: is the rate at which charges pass a given point◦ A/C: continually shift from flowing in one direction

to flowing in the reverse direction Example: Electricity from the outlet in a house

◦ D/C: the charges always flow in the same direction Example: electricity from a battery

17.2 Electric Current and Electrical Energy

Voltage: the potential difference between two points; measured in volts◦ How much work is needed to move a charge

Resistance: in physical science, the opposition presented to the current by material or device

17.2

Resistance, Thickness, and Length

17.2

Cells: in electricity, a device that produces an electric current by converting chemical or radiant energy into electrical energy

17.2