Physics Test 1

• North Star
• Does not move
• Polaris is on the same axis as the earth

• The apparent backward motion of objects in the sky
• Caused by the earth moving faster than other objects further away from the sun

• Idea that the Earth is the center of the solar system
• Ptolemy's Idea, Ptolematic system
• Orbital patterns thought to be circular

• Idea that planets revolve around the sun
• Copernicus' Idea, Copernican system
• Orbital Patterns still thought to be circular

• Made incredible observations with crude instruments
• Had most advanced instruments of the time

• Three Laws
• 1. Paths of planets around the sun are ELIPSES with the sun as focus. (Planetary motion, Eliptical Foci)
• 2. Planet moves slower when further away from the sun, sweeping equal amounts of area in the same amount of time.
• 3. Time taken for 1 orbit is related to distance from the sun

• Newton's Law
• The FUNDAMENTAL FORCE that explains all motion that can be observed in the universe

Acceleration due to gravity (on earth) is only in an up/down direction

Gravity attractions between the sun and moon

• Larger
• At new moon and full phase
• The sun and moon's gravity pull in the same direction

• Weaker
• Angle of gravitational pull of moon and sun is a right angle
• 1st and 3rd quarter phases

British Imperial

• Systeme Internationale
• S.I./ Metric System
• Ex. Meters kilograms

• A change in position
• Everything in the universe is in constant motion

• How fast the location of any object is changing
• Rate of change of position
• Instantaneous Speed: speed traveling at during one moment of time. (Ex. Spedometer in car)
• Scalar quantity

• A quantity at wich only magnitude is specified
• Time, mass, speed, temperature

• A quantity in which both magnitude and direction is specified
• Velocity, Acceleration, Weight (Gravity too)

• Represented by an arrow
• Length of arrow = magnitude of vector
• Arrow head points in the direction of the vector

Have direction: North, east, 45 degrees

• Rate of change of velocity
• Acceleration is negative if it is opposite to the motion of the object

• If it increases in magnitude (5 m/s -> 15 m/s)
• Decreases in magnitude
• Changes direction

• Velocity of a falling object is proportional to the length of time that the object has been falling
• In the abscence of air, all things fall the same rate

• Wanted to know why things move
• Developed the idea of FORCE

• A pull or push constitutes a force
• Units: Newton (N) or Pound (lb)
• Vector Quantity
• At any time, there may be several forces acting on an object: Net Force

Force due to gravity

• Object moves with constant velocity
• Net Force = 0

• Velocity isn't constant... object accelerates
• Net force does not equal 0

• Object's resistance to change and motion
• Greater mass = greater inertia

• 1. Law of Inertia: if Fnet= 0, a body at rest will stay at rest
• 2. If there is a net force, the object accelerates
• 3. Action-reaction: For every action, there is equal opposite reaction. Forces come in pairs.

• Static Friction: Non-moving
• Kinetic friction-moving
• In order to get an object moving we must overcome static friction
• Rougher materials have greater frictional forces
• Frictional forces always oppose the motion of the object

• Friction during free fall means net force is reduced
• As velocity increases, so does frictional force
• Frictional force= weight force, net force=0

An object in freefall will fall at a constant velocity when air resistance is involved

• "Center seeking" force
• The direction is always toward the center of any curved pattern
• Changing in direction... accelerate.
• In circular motion, there is always a different velocity (vector, changing direction), but the speed (scalar) remains constant

• The gravitational force of attraction between two objects

• Done whenever a force causes a motion or a change in motion
• Scalar quantity
• W= fd (F=ma)
• Work against Gravity: Wg=mgh
• Something has to move
• Force must be the force along the direction of motion
• Unit: Nm or Joule

• The ability to do Work
• Work done = energy used

• The rate at which work is done
• Unit: J/S or 1 Watt
• Watts over time

• Energy an object has due to motion
• No velocity, no KE
• Larger mass or velocity, larger KE
• Double Velocity, KE increases 4x

• Gravitational Energy/ Gravitational Potential Energy
• Energy an object has due to its position above the ground
• GPE= mgh

Due to object's position in a magnetic feild

May change from one form to another, but the total amount of energy in the universe is constant