23 terms

# Excelsior Physics Unit 2

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Equilibrium
The state of having zero net force being acted upon an object at rest. When all the forces acting on an object are balanced, or when the sum of the +x forces on an object equals the sum of the -x forces.
Force
Any push or pull. The more an object weighs, the more force is acting upon it, and contrarily, the less an object weighs, the less force is acting upon it.
Friction
Name given to the force that acts between materials that touch as they move past each other. For example, a puck sliding across a street comes to rest faster than across ice because there is more friction with the street than with the ice. The same is true for the dishes on a tablecloth. You can very quickly pull the tablecloth out from underneath the dishes without moving the dishes because the dishes want to stay at rest and the friction caused by the force of the quickly moving tablecloth isn't enough to make the dishes fall down because of their own inertia (there own desire to remain at rest).
Inertia
The resistance an object has to a change in its state of motion. Galileo's experiments with smooth planes, which showed that a ball dropped from a certain height would roll up the other side to the same height confirmed this idea of inertia. The dishes on the table when the tablecloth is quickly removed do not fall down because they have inertia. They are unwilling to change their own state of motion which is at rest.
Kilogram
The SI unit of measurement of weight whose symbol is kg
Law of Inertia
Another name for Newton's first law: states that every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.
Mass
The quantity of matter in an object.
A measure of inertia.
Not the same as weight or volume.
Depends only on the number and kind of atoms it has in it.
Does not depend on the location of the object.
The more mass an object has, the greater its inertia and the more force it takes to change its state of motion.
Net Force
The combination of all forces acting on an object. When more than one force acts on an object, the net force or resultant force is the sum of the forces. When forces act in the same direction, that is the maximum resultant and you would add the forces together. When forces act in opposite directions, that is the minimum resultant and you would subtract the forces.
Newton's first law
Another name for the law of inertia: states that every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.
normal force
another name for support force: the equal and opposite force needed to balance an object's weight at rest.
support force
another name for normal force: the equal and opposite force needed to balance an object's weight at rest.
Weight
The force of gravity on an object.
Depends on the location of the object.
Mass is not Weight. Mass doesn't change no matter where the object is. For example, if you weigh 100 pounds on Earth, you would weigh less in space or on the Moon, however, your mass stays exactly the same.
Newton
The SI unit of force. One newton is equal to slightly less than a quarter pound. The symbol is an N. If you know the mass of something in kilograms, and want its weight in newtons, multiply the number of kilograms by 9.8. If you know the weight in Newtons, divide by 9.8 to find the mass in kilograms.
Newton's Second Law
The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is the same direction as the net force, and is inversely proportional to the mass of the object. In equation form, acceleration = net force/ mass.
Pressure
The amount of force per unit of area. Measured in pascals (Pa). In equation form, pressure = force/ area of application. Force is measured in Newtons. In order to keep velocity constant, the force applied must remain the same as well.
Sir Isaac Newton
The first person to quantify gravity. He figured out that apples fall from trees because of Earth's gravity. He also figured out that the moon travels in a curved path around the Earth also because of the Earth's gravity.
Acceleration
Acceleration = net force / mass. Force creates acceleration. If the force stays the same, but the mass changes, the acceleration will change inversely as well. So, if the mass increases, the acceleration will decrease. Conversely, if the mass decreases, the acceleration would increase.
Newton's Third Law
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. Laws are ALWAYS true.
Action and Reaction
There are actions and reactions everywhere in the universe. During a free fall, the object falling is simultaneously exerting a force on the earth while the earth is exerting a force on the object. Gravity figures heavily in these forces. The forces between the object and the Earth are exactly the same, however, their masses are vastly different, so their movements appear quite different as well. The object appears to fall to the Earth, and the Earth appears to not move, but in reality it does (an infinitesimal amount). Rocket propulsion works in a similar way. It continually recoils from the exhaust gases ejected from its engine.
Aristotle
Aristotle was the foremost Greek scientist. He studied motion and divided it into two types: natural motion and violent motion. Natural motion was essentially gravity, straight up or down. Violent motion has imposed motion like being pushed or pulled.
Terminal Velocity
Whenever objects fall in our atmosphere, friction is caused by air resistance. When the air resistance equals the weight of the object, the net force is zero and acceleration stops. This is known as terminal velocity. In this case, heavier objects fall at faster rates than lighter objects because they accumulate more acceleration as the air resistance builds towards their weight.
Vector Forces
Force, like velocity, is a vector quantity with both magnitude and direction. The farther away from vertical the angle goes, the higher the magnitude of the tension force must also increase for the diagonal to remain capable of holding the same force. When a load hangs from a vertical, a single force needs to pull with at least the same force as the weight of what needs to be held. If more forces are used to hold the load, then each force only needs to hold part of the total weight. So, for example, if you need to hold 100 N and you have 4 forces to hold it, each force must hold at least 25 N because it can distribute the weight.
Gravity and Distance: The Inverse-Square Law
This law applies to the weakening of gravity with distance along with other natural processes. It says that a quantity varies as the inverse square of its distance from it source. Therefore, if an object weighs 1 N at Earth's surface, it will weigh 1/2^2 or 1/4 when it moves twice as far away from Earth's center. If it moved three times as far away, it would weigh 1/3^2 or 1/9. If it moved four times as far away, it would weigh 1/4^2 or 1/16. The reverse holds true if you were to get closer to the Earth's center. Technically, the closer you get to the center of the Earth, the more you would weigh.