Physics Unit 1: Motion

Motion

A change in position of an object with respect to time. Motion is typically described in terms of displacement, distance (scalar), velocity, acceleration, time and speed.

"Mechanics"

A description of how a body changes its position in space during a period of time

Gravity

A force that applies a net force on a falling body equal to the body's weight causing the body to accelerate at approximately 10 m/s2.

Friction

A force that opposes motion and consists of static (micro-welding) and kinetic (sliding). Air resistance is a form of friction that increases as the speed of the object increases.

Field

A region in which each point is affected by a force. Objects fall to the ground on Earth because they are affected by the force of Earth's gravitational field.

Speed

A scalar quantity measuring the rate at which an object covers distance. Speed is ignorant of direction.

Velocity

A vector quantity, combining an object's speed as well as its direction. For most of this year's purposes, velocity is used as speed.

Aristotle on motion

All motions are due to the nature of the moving object or due to a sustained push or pull. If an object's natural tendency is to stay at rest, it will eventually stop moving after its initial force. To stay in motion infinitely, an object needs an infinite push/pull. Believed that a vacuum was impossible.

Average speed, instantaneous speed

Average speed of an object in an amount of time is the object's overall distance covered divided by the time it took for the object to do so. Instantaneous speed is an object's speed at any one instant; equivalent to literally stopping time and measuring the speed of the object

Galileo on motion

Concerned with how things move rather than why they move. Stated that if there is no interference with a moving object, it will keep moving in a straight line forever; no push, pull, or force of any kind is necessary. Used inclined planes to show that a ball moving down an incline will resist forces and end up going as high on a second incline as its starting height (discovering inertia). Also found from dropping objects of various weights off of the leaning Tower of Pisa that when air resistance is negligible, everything falls at the same of rate 10 m/s2. Newton later refined of Galileo's ideas into his first law of motion (inertia), and used others for the basis of his other laws.

Distance and displacement

Distance is a scalar quantity that refers to "how much ground an object has covered" during its motion. Displacement is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.

Einstein on time

Einstein theorized that time has a potential to be altered if the right circumstances are met. For example, time always appears to tick on at the same rate for us on Earth, but, for example, if one person stood at the event horizon of a black hole and another person stood on earth, the person in the black hole would appear to be moving incredibly slow to the person on earth, while the person on earth would appear to be moving incredibly fast to the person in the black hole. Basically, he thought that time is relative any point's physical properties.

Gravitational mass

F = G m1 m2/r2 Where G is the universal gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between them. This, in effect defines the gravitational mass of an object.

Newton's third law

Forces exist only in pairs and these pairs are equal and opposite

What is gravity?

Gravity is a force pulling together all matter (which is anything you can physically touch). The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly. It is one of the weakest forces in the universe, yet can sum together to become one of the strongest.

Action at a distance

In physics, action at a distance is the concept that an object can be moved, changed, or otherwise affected without being physically touched (as in mechanical contact) by another object.

Newton's first law

Inertia; an object's property to resist changes in motion

Inertial mass

Inertial: A measure of an object's mass found by measuring its inertia. Mainly defined by F = ma, found by applying a force of F Newtons to an object, measure the acceleration in m/s2, and F/a will give you the inertial mass m in kilograms.

Projectile motion

Motion of any object that, once given its initial velocity, is only only acted upon by gravity

Newton's second law

Net forces cause changes in motion

Newton on time

Newton theorized tat time is something completely separate from any possible physical alteration; it ticks on at the same rate no matter the point in space.

Net Force

The overall force being applied to an object. Net forces cause a change in motion. A net force of zero causes no change in motion, but an object will continue in its state of motion.

Acceleration

The rate of change of velocity of an object. For example, a car can drive 15 miles in 2 hours, or the same distance in one hour. Its acceleration is faster in one hour.

Free Fall Table (6 seconds)

Time V(instaneous) Distance fallen 1s 10m/s 5m 2s 20m/s 20m 3s 30 m/s 45m 4s 40 m/s 80m 5s 50m/s 125m 6s 60m/s 180m

What is time?

Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them.

Scalars and Vectors

Ways of defining attributes using magnitude (size) and/or direction. Ex: weight is a vector (it has magnitude and direction-down) while mass is a scalar (it has only size, but no direction).

Distance Fallen equation

d = 5t^2

V(instantaneous) equation

v = at (a = g = 10)