29 terms

# Physics Unit 1

#### Terms in this set (...)

power
Definition
the ratio of the amount of work done per unit of time, or the rate at which energy is transferred or transformed
Key Context
You and a friend are moving two heavy boxes by pushing them. Both boxes have the same mass (weight). You both push them the same distance. But you get yours there faster. That means you used more power to move your box. All power is measured in watts. The electric meter at your home tells how many kilowatts of power is used.
momentum
Definition
a quantity of how much inertia a dynamic object has
Key Context
The total momentum in a closed system is constant. If the momentum of an object changes it must have been acted upon by a force.
Greek/Latin Etymology
Latin meaning "movement or moving power"
centripetal force
Definition
any force that causes centripetal acceleration
Key Context
A pendulum swings because tension pulls the bob in an arc. If left alone, the bob would move in a straight line, but the string "pulls" the bob into an arc. The tension is a centripetal force causing the direction of the bob's path to change.
Greek/Latin Etymology
Latin root centri meaning "center" and petal meaning "to fall"
displacement (vector)
Definition
a length vector pointing from an object's starting point to its ending point
Key Context
Displacement, unlike distance, is concerned only with the difference between an object's starting and ending points. The displacement is a vector. You can find the displacement by subtracting the initial position from the final position.
Greek/Latin Etymology
Latin prefix dis- meaning "away"
scalar
Definition
a quantity that is measured by its magnitude (amount) but has no direction
Key Context
The amount of mass in an object is a scalar quantity since every object has a distinct amount of mass. The mass has no direction associated with it. For instance, it would make no sense to say that a laptop has a mass of 2.5 kg, North. Direction is relevant only for vector quantities, such as velocity or force.
energy
Definition
the ability to do work or cause change; can be stored in chemicals found in food and released to the organism to do work
Key Context
Your body constantly uses energy, which comes from the food you eat. As food is consumed, your body stores the energy in your muscles until you need it.
Greek/Latin Etymology
Greek prefix en- meaning "at"; Greek root ergon meaning "work, that which is wrought; business; action"
uniform circular motion
Definition
motion that is both circular and at constant speed
Key Context
Uniform circular motion implies that the motion takes place in a circular path and that the speed of the object is constant throughout the motion. The direction of the motion is changing constantly as the object turns, but the speed does not.
speed
Definition
the rate at which distance is traveled
Key Context
Speed is a measure of how fast something is moving. It can also be thought of as a rate—the rate at which the object travels a distance. A girl running at twice the speed of another girl in a race travels twice the distance in the same amount of time.
work
Definition
the change in a system's kinetic energy due to being acted on by a force
Key Context
Work is a measure of how much energy is exerted on an object. If a constant force F is applied over a distance d, then the work W is given by W = fd.
free body diagram
Definition
a diagram showing all the forces acting on an object
Key Context
To study the motion of an object, physicists like to know all the forces acting on an object. A free body diagram (often abbreviated as FBD) is used to show all the forces acting on a single object. Forces (that are vectors) should be represented with arrows originating from the center of the object.
acceleration due to gravity
Definition
the change in velocity caused by a gravitational force
Key Context
A gravitational force can cause the velocity of a moving object to increase, decrease, or change direction. For example, Earth exerts a gravitational force that acts on objects near its surface. This force causes an object thrown upwards to eventually fall towards the center of Earth. The change in velocity due to this force is acceleration due to gravity.
force
Definition
an interaction between objects that causes a change to the objects' motion.
Key Context
Magnitude and direction are equally important when describing a force.
acceleration
Definition
a change in velocity over time
Key Context
An object's velocity can increase, decrease, or change direction. These changes in velocity are described as acceleration.
velocity
Definition
a vector quantity that indicates both the rate at which displacement changes and the direction of motion
Key Context
Velocity is a vector formed by computing the displacement per unit time. It indicates both how fast an object is moving and in which direction.
vector
Definition
a quantity with components of both magnitude and direction
Key Context
Scalar quantities measure only magnitude, but vector quantities measure both magnitude and direction. Speed is a scalar quantity equal to the magnitude component of velocity. Velocity also includes directional information, so it is expressed as a vector.
Greek/Latin Etymology
Latin stem vector meaning "carrier"
center of gravity
Definition
the average location of the weight of a system
Key Context
The center of gravity is defined as that point in an extended body which moves in a gravitational field as if all the mass were concentrated at that one point.
center of mass
Definition
the average location of the mass of a system
Key Context
The center of mass can be described as the average location of the mass of the object. If the force of gravity is acting consistently on the entire object, the center of gravity will be the same as the center of mass.
instantaneous velocity
Definition
the rate of motion of an object traveling in a specified direction at a point in time
Key Context
If an object's instantaneous velocity is not constant, its average velocity will be be different from its instantaneous velocity. The photo-finish of a horse race can give a measure of each horse's instantaneous velocity.
Greek/Latin Etymology
From the Latin instantem, meaning "pressing" or "urgent" and from the Latin velocitas, meaning "speed" or "swiftness"
instantaneous speed
Definition
the rate of motion of an object at a point in time
Key Context
The speedometer of a motor car provides a reading of the vehicle's instantaneous speed. Instantaneous speed is measured in units of distance per unit time.
Greek/Latin Etymology
From the Latin instantem, meaning "pressing" or "urgent" and from the Old English sped, meaning "advancement"
static friction
Definition
a resistive force between stationary objects due to the roughness of the two surfaces in contact
Key Context
Objects that appear smooth are actually quite rough when you examine them on a microscopic level. This roughness makes it difficult for two objects to slide past each other. This resistive force is called friction. Static friction is the type of friction that exists between two touching stationary objects.
Greek/Latin Etymology
Latin root stat- meaning "stand"
frame of reference
Definition
an item against which the motion of an object can be measured
Key Context
Motion might appear different from different frames of reference. For example, a person standing at a bus stop sees the motion of a car differently than the car's passengers see the same motion. From the frame of reference of the bus stop, a diagram of the car's displacement between points A and B might look like a horizontal line. From the frame of reference of the passenger, the displacement might be zero.
Newton's law of universal gravitation
Definition
the law that states that the magnitude of the gravitational force increases as the mass of the two objects increases and decreases as the distance between the objects increases
Key Context
When two objects interact, the gravitational force acts on both of them with equal strength but in opposite directions. For example, the gravitational force between Earth and the Moon is very large because the mass of these bodies is large. The force pulls the Moon toward Earth, and it pulls Earth in the opposite direction—toward the Moon—with equal magnitude.
non-inertial frame of reference
Definition
coordinate system and set of points that depend on the location and orientation of objects in space and time
Key Context
An outside observer is in a non-intertial frame of reference with respect to someone inside an elevator who does not experience motion because they are in the inertial frame of reference. The laws of motion vary according to the observer's location with respect to a non-inertial frame of reference.
Greek/Latin Etymology
From the Latin inertia, meaning "idleness" or "inactive" and from the Latin referentem, meaning "in a book or passage" (The meaning of "frame" derives from Middle English.)
inertial frame of reference
Definition
coordinate system and set of points to independently locate and orient objects in space and time
Key Context
Motion inside an elevator is within an inertial frame of reference so that the observer does not detect motion within the elevator. The inertial frame of reference is a a key concept in general relativity.
Greek/Latin Etymology
From the Latin inertia, meaning "idleness" or "inactive" and from the Latin referentem, meaning "in a book or passage" (The meaning of "frame" derives from Middle English.)
Newton's laws
Definition
the three fundamental laws Isaac Newton discovered governing the motion of objects
Key Context
Newton's first law states: "An object in motion stays in motion, unless acted on by a force. An object at rest stays at rest unless acted on by a force." Newton's second law states: "Force is the product of mass and acceleration." Newton's third law states: "For every action force, there is an equal but opposite reaction force."
equilibrium
Definition
state of balance between all parts of a system
Key Context
Objects in equilibrium have no net force acting on them. For instance, a laptop resting on a table is in equilibrium because the force of gravity pulling it down is balanced by the normal force of the table pushing it back. The sum of these forces is zero.
Greek/Latin Etymology
Latin root aequi meaning "equivalent" and libr "a balance."
inertia
Definition
an object's resistance to a change in motion
Key Context
In outer space, there is no atmosphere or friction. Satellites travel around the earth without stopping. This is because of inertia. Objects on Earth come to a stop because they are affected by friction or gravity.
net force
Definition
the resulting force determined by combining all of the forces acting on an object
Key Context
When a person kicks a soccer ball, there are several forces acting on the object. First, are the forces of gravity and normal force. These two forces will oppose one another and cancel each other out. Next, is the force of friction. This is the force that is holding the soccer ball back and slowing it down. Finally, is the force applied to the ball that is created by the person kicking it. In the end, the net force on the ball will be positive in the direction that it is kicked, as it would be greater then the frictional force. When objects are at a constant velocity, the net force is considered to be zero, as all forces are equal.
average speed
Definition
the distance traveled by an object divided by time it traveled
Key Context
Objects change speed frequently. Therefore, to determine how far an object travels over a time period in which its speed is changing, it is often useful to determine the average speed over a period of time.
STUDY GUIDE

#### Flickr Creative Commons Images

Some images used in this set are licensed under the Creative Commons through Flickr.com.
Click to see the original works with their full license.