phyc test 2

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dynamics

is the study of the causes of motion

net force

refers to the vector sum of all forces acting on an object

newtons first law of motion

is also known as galileo's law of inertia, inertia refers to the tendency change an object to resist any change in its state of motion. Inertia is measured by measuring an objects mass

Newtons second law of motion

refers to an object's motion when a net force does not equal zero. The net force (F) will cause an object to accelerate or decelerate. The rate of acceleration (a) is directly proportional to the magnitude of the force and inversely proportional to the object's mass

Newtons third law

states that whenever one object everts a force on a second object, the second object exerts an equal but opposite force on the first

weight

is a measure of the force of gravity on an object

friction

is a contact force that opposes the relative motion of two surfaces as they slide past each other. The frictional force depends on the coefficient of friction and the normal force

coefficient of friction

is a pure number without physical units and varies with the types of surfaces that are in contact.

When the object is at rest, the coefficient of static friction

is used to determine the magnitude of the frictional force just before the object starts to move

When the object is moving

the coefficient of kinetic friction is used

If the net force of an object equals zero, the the objects motion will not change

Newtons fist law

Newtons first law mathematical formula

-> ->
Net F =0 or E F=0

An object's acceleration is related to the net force and the objects mass

Newton's Second Law

Newton's second law mathematical formula

-> ->
a= E F/M OR EF=m a

If object 1 exerts a force on object 2 then object 2 exerts an equal but opposite force on object 1

Newtons third law

Newtons third law mathematical formula

-> ->
F12=-F21

An object's weight is directly proportional to its mass and gravitational acceleration

weight

weight mathematical formula

-> ->
w= m g

Frictional force depends on the coefficient of friction and the normal force

force of friction

force of friction mathematical formula

Ffr-m Fn

The SI unit of force is the

newton (N)

inertia is

the tendency of an object to resist any change in its state of motion

A stone hangs be a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone. If a person gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it?

if a person gives a sharp pull to the dangling thread, the inertia of the stone resists any change in its motion. The result is that the stone does not move and the force exerted by the person is not transmitted to the section of thread above the stone. The tension in the section below the stone is much greater than above the stone and the lower section snaps.

A stone hangs be a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone. If a person gives a slow and steady pull

If a person exerts a slow and steady pull, the inertia of the stone is overcome and the stone will begin to move slowly. The tension in the section of thread is due to the person. THe tension is the section nabove the stone is due to the sum of the pull exerted by the person and the stone's weight.

The force of gravity on a 2-kg rock is twice as great as that on a 1-kg rock. Why then doesn't the heaviest rock fall faster?

Newton's second law; A 2 kg rock has twice as much weight as a 1 kg rock but it also has twice as much mass i.e. inertia and is twice as hard to accelerate. The ratio fo the force to mass is the same for both object and as a result the acceleration is the same for each.

When you stand still on the ground, how large a force does the ground exert on you? Why doesn't this force make you rise up into the air?

The downward force of your weight is balanced by an equal and opposite force exerted by the ground. The net force on your body is zero, your rate of acceleration is zero, and you remain motionless. As a result, you neither rise nor fall

Whiplash sometimes results from an automobile accident when the victim's car is struck violently from the rear. Explain why the head of the victim seems to be thrown backward in this situation. Is it really?

When the car is struck from the rear, the force on the car causes the car to move forward.The seat and seatback are attached to the body of the car and move forward with the car. As the seatback moves forward it pushes the occupant's torso forward.The person's head tends to remain at rest while the car plus victim's torso is pushed forward

Weight varies slightly

from place to place on the surface of the Earth

Mass depends on an

object's inertia and does not vary with location

Weight is the

force of gravity acting on an object and varies from place to place

A person standing on the Earth weighs six times as much

as he or she would on the moon; however his or her mass would remain the same

THe normal force is a contact force that

acts perpendicular to the common surface of contact

A book at rest on a horizontal table is acted upon by two forces,

the book's weight is downward but is opposed by the normal force which is equal in magnitude by upward, perpendicular to the surface of the table

A heavy crate rests on the bed of a flatbed truck.When the truck accelerates, the crate remains where it is on truck, so it too accelerates. What force causes the crate to accelerate

The net force on the crate is due to static friction. In order for the crate to remain at rest relative to teh surface of the bed of the truck,the frictional force must be sufficient to cause the crate to accelerate at the same rate as the truck.

Friction force on sled exerted by ground

Fsg

force on ground exerted y sled

-Fsg

as long as there is no frction

no net force acts on the object

kinetic friction

sliding friction

Kinetic friction mathematical equation

Ffr=mkFn

When an object is pulled by an applied fore along a surface,

the force of friction Fr opposes the motion. The magnitude of Ffr is proportional to the magnitude of the normal force (Fn)

A hammer exerts a force on the nail, and the nail exerts a force back on the hammer is in accordance

with Newton's third law

If your hand pushes against the edge of a desk

is in accordance with Newton's third law

The launch of a rocket is in accordance with

Newton's third law

When an iceskater pushes against the railing, the railing pushes back and thsi force causes her to move aw

in accordance with Newtons third law

uniform circular motion

occurs when an object travels in a circle at constant speed

tangential velocity

refers to the direction of the velocity vector of an object as it travels in a curved path. The velocity vector is tangent to the path at each point in the curve

tangential acceleration

refers to the change in speed per unit time of an object as it travels in a curved path. The tangential acceleration is directed tangent to the path at each point

Centripetal acceleration or radial acceleration

is the inward radial acceleration experienced by an object traveling in a circle. The direction of the acceleration vector is perpendicular to the direction of the velocity vector

period (T)

of the circular motion is the time required for an object to complete one revolution

frequency of rotation (f)

is the number of repititions of the motion per unit time.The frequency is inversely related to the period of the motion

centripetal force

is the term used for the force acting toward the center of the circle. the centripetal force is not some new kind of force

centripetal force means

that the force is directed toward the circle's center. The force must be applied by some external agent

Newtons universal law of gravitation

is the force of attraction between any two objects due to their mass. The law states that the magnitude of the force between two particles is directly proportional to the product of their masses and inversely proportional to the square distance between their centers

Kepler's first law

states that the path of each planet about the Sun is an ellipse with the SUn at one of the focal points of the ellipse

Kepler's second law

states that each planet moves such that an imaginary line drawn from the Sun to the planet sweeps out equal areas in equal periods of time

Kepler's third law

states that the ratio of the squares of the periods of any two planets revolving about the Sun is equal to the ratio of the cubes of their average distance from the Sun

aR=V^2/r

centripetal or radial acceleration (aR) as related to the tangential velocity (v) and the radius of the circle (r)

f=1/T; T=1/f

frequency of rotation (f) is inversely related to the period (T) of the motion

weight

*force of gravity exerted on object
*varies depending on location and g
*vector
*spring scale

mass

*quantity of matter
* constant everywhere
*measure in kilogram
*balance
*beam or electronic

3 differences of uniform circular

* is at constant speed,
* needs a net force acting on it
*centripetal acceleration- center seeking

3 differences of non uniform

*is not at constant speed
*tangential component of a force is acting

how centrifuge works?

high speed device separates mixture by gravitation centripetal force separates particles for you, heavy particles resist circular motion (inertia) lighter particles conform to the motion. The heavier particles go to the bottom, the lighter particles float to the top. If the particle reaches the bottom of the tube, then the bottome exerts a force that keeps the particles moving in a circle. Fr=mv2/t as V increases, F increases. If V gets too high, the force will break the tube

Four fundamental forces

1)gravity 2) electromagnetism 3) weak nuclear force

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