# Conceptual Physics Study Guide

Centripetal Force
Center-directed force that causes an object to follow a curved or circular path

Centripetal Acceleration
Center-directed acceleration on an object moving in circular motion

Component of a Vector
Parts into which a vector can be separated and that act in different directions from the vector

Work
The product of the force on an object and the distance through which the object is moved (when force is constant and motion is in a straight line in the direction of the force)

Unit of Measurement: Work
Joules

Energy
That which can change the condition of matter.
The ability to do work.

Power
Rate at which work is done or energy is transformed, equal to the work done or energy transformed divided by time. P=W/t

Unit of Measurement: Power
Watts

Kinetic Energy
Energy of motion, equal (nonrelativistically) to mass multiplied by the square of the speed, multiplied by the constant 1/2. KE = 1/2mv^2

Potential Energy
Energy of position, usually related to the relative position of two things, such as a stone and the Earth (gravitational PE) or an electron and a nucleus (electrical PE)

Momentum
Inertia in Motion. The product of mass and the velocity of an object (provided the speed is much less than the speed of light). Has magnitude and direction and therefore is a vector quantity. Also called linear momentum and is abbreviated “p”

Impulse
The product of force and the time interval during which the force acts. Produces a change in momentum. (Force x Time)

Weight
The force that an object exerts on a supporting surface (or, if suspended, on a supporting string)–often, but not always due to the force of gravity.

Elastic Collision
Collision in which colliding objects rebound without lasting deformation or heat generation

Inelastic Collision
Collision in which colliding objects become distorted and/or generate heat during collision, and possibly stick together

Reaction Force
Force that is equal in strength and opposite in direction to the action force, and one that acts simultaneously on whatever is exerting the action force.

Rotational Inertia
Reluctance or apparent resistance of an object to change its state of rotation, determined by the distribution of mass of the object and the location of the axis of rotation or revolution.

Torque
Equal to the force x lever arm distance

Center of Mass
Point at the center of an object’s mass distribution, where all its mass can be considered to be concentrated

Angular Momentum
Product of a body’s rotational inertia and rotational velocity about a particular axis. For an object that is small compared with the radial distance, it is the product of the mass, speed, and radial distance of rotation.

Escape Speed
Speed (velocity) that a projectile must reach to escape the gravitational influence of Earth or the celestial body to which it is attracted.

Ellipse
Closed curve of oval shape wherein the sum of the distances from any point on the curve to two internal focal points remains constant

Contributions of Aristotle
How heavy an object is determines how fast it will fall.
Violent vs. Natural

Contributions of Aristarchus
Suggested that the Earth spins on a daily axis (accounts for the motion of the stars). Earth and the other planets move annually around the sun. Measured moon’s diameter and distance from Earth.

Contributions of Tycho Brahe
Mentored Kepler.
Directed world’s first great observatory.
Accurately measured the positions of over 20 planets.

Cavendish
Found the proportionality constant G, the universal gravitation constant.
(Done my measuring the tiny force between lead masses with an extremely sensitive torsion balance)

Copernicus
Proposed that the sun is the center of the solar system, not the earth, and that the earth revolves around the sun.

Galileo
Inertia
Disproved much of Aristotle’s work with the leaning tower drops and slope experiments

Kepler
Devised Laws of Planetary Motion
Coined term, “satellite”

Newton
Formulated the Laws of Motion
Formulated law of universal gravitation

Ptolemy
Improved the earth-centered theory

Newton’s Third Law of Motion
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first

Newton’s Law of Universal Gravitation
Every body in the universe attracts every other body with a force that, for two bodies, is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them. F=G(m1m2)/(d^2)

Kepler’s First Law of Planetary Motion
The path of each planet around the Sun is an ellipse with the Sun at one focus

Kepler’s Second Law of Planetary Motion
The line from the Sun to any planet sweeps out equal areas of space in equal time intervals

Kepler’s Third Law of Planetary Motion
The square of the orbital period of a planet is directly proportional to the cube of the average distance of the planet from the Sun

Momentum Conservation
In the absence of an external force, the momentum of a system remains unchanged. Hence, the momentum before an event involving only internal forces is equal to the momentum after the event.

Conservation of Energy
Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes

Work-Energy Theorem
The work done on an object equals the change in kinetic energy of the object

Conservation of Angular Momentum
When no external torque acts on an object or a system of objects, no change of angular momentum can occur. Hence, the angular momentum before an event involving only internal torques or no torques is equal to the angular momentum after the event.