physics 1310 exam 2 texas state- xiao | Quizlet

momentum

inertia in motion, a property of moving things

momentum=

mass x velocity

momentum in equation form

p=mv

a moving object has

momentum, kinetic energy and speed

when the speed of an object is doubled, its momentum

doubles

impulse

a change in momentum

impulse=

force x time interval

impulse in equation form

J=Ft

when the force that produces an impulse acts for twice as much, the impulse is

doubled

if you push with the same force on something for twice the time, its change in momentum is

doubled

when dish falls, will the change in momentum be less if it lands on carpet than if it lands on a hard floor?

No, both are the same

impulse is

a vector (in the same direction of F)

forces are

internal, cancel to zero

impulses are

internal, cancel to zero

momentum is

a vector (in the same direction of v)

law of conservation of momentum

if no net external force acts on a system, the momentum of the system remains unchanged

momentum is conserved in collisions

the net momentum of a system of colliding objects is unchanged before and after the collision

elastic collison

-occurs when colliding objects rebound without lasting deformation or any generation of heat

-momentum is transferred from one to the other

inelastic collision

-occurs when colliding objects result in deformation and/or the generation of heat

-objects stick together

work=

force x distance

work in equation form

W=Fd

Work is done in lifting a barbell. How much work is done in lifting a barbell that is twice as heavy the same distance?

twice as much

You do work when pushing a cart with a constant force. If you push the cart twice as far, then the work you do is

twice as much

work*

Only the component of force parallel to the motion contributes to work

power

the rate at which work is done

power in equation form

P=W/t

mechanical energy

energy due to position or to motion, or both

two forms of mechanical energy

potential, kinetic

kinetic energy

energy of motion

kinetic energy in equation form

KE=1/2mv^2

if object speed is doubled, its kinetic energy is

quadrupled

potential energy

stored energy held in readiness with a potential for doing work/being converted into other forms of energy

two kinds of potential energy

spring/elastic, gravitational

spring potential energy

potential energy stored as a result of deformation of an elastic object

gravitational potential energy

potential energy due to the position above a reference level

gravitational potential energy in equation form

PEg=mgh (first g is superscript)

work-energy theorem

net work= change in kinetic energy

law of conservation of energy

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

efficiency

percentage of work put into a machine converted into useful work output

efficiency in equation form

efficiency=useful energy output/total energy input

a certain machine is 30% efficient. this means the machine will convert

30% of the energy input to useful work--- 70% of the energy input will be wasted

momentum and kinetic energy compared

-both are properties of moving things

-momentum is a vector and can be canceled

-kinetic energy is a scalar and can never be canceled

rotational motion

the motion of an object that turns about an internal axis

circular motion

the motion of an object that moves in a circular path

tangential speed (linear)

distance traveled per unit of time (symbol v, unit: m/s)

rotational speed (angular)

angular displacement per unit of time (symbol w, unit: rad/s)

tangential speed=

rotational speed x radial distance

v=wr

all points on a rotating object

have the same rotational speed

points closer to the circumference

have a higher tangential speed than point closer to the center

A ladybug sits halfway between the rotational axis and the outer edge of the turntable. When the turntable is rotating and the bug has a tangential speed of 2 cm/s, what will be the tangential speed of her friend who sits at the outer edge?

4 cm/s

rotational inertia (symbol I)

property of an object to resist change in its rotational state of motion

the greater the rotational inertia of an object

the harder it is to change its rotational state

rotational inertia depends on

-mass

-distribution of mass about the axis of rotation

the greater the distance between an object's mass concentration and the axis

the greater the rotational inertia

rotational inertia

the same object has different rotational inertias about different rotational axes

torque

change the rotational motion of objects

(torque) the ability of a force to cause a rotation depends on

-magnitude of the force

-the point at which the force is applied

-the direction in which it acts

torque=

lever arm x force

torque in equation form

t=rF

lever arm

the perpendicular distance from the pivot to the applied force (the line along which the force is applied)

center of mass

average position of all the mass that makes up the object

center of gravity (CG) is

average position of weight distribution

center of gravity

-usually refer to the same point of an object

-a symmetrical object has its CG at its geometrical center

-non-uniform, irregularly shaped bodies

locating the CG

-suspend the object from a point and draw a vertical line from suspension point

-repeat after suspending from another point

-the center of gravity lies where the two lines intersect

stability

-draw a line straight down from the center of gravity

-if it falls inside the base of the object, it is stable

-if it falls outside the base, it is unstable

centripetal force

a force that makes an object move in a circular path and it is directed toward the center of the circular path

centripetal force in equation form

centripetal force= mass x tangential speed^2/ radius

Suppose you double the speed at which you round a curve, by what factor must the centripetal force change to prevent you from skidding?

four times

Suppose you take a sharper turn than before and halve the radius, by what factor will the centripetal force need to change to prevent skidding?

double

centrifugal force

an object in a rotating system seems to experience an outward force

angular momentum

-rotational inertia x rotational speed

-equation form: L=lw

law of conservation of angular momentum

If no external net torque acts on a rotating system, the angular momentum of that system remains constant

Suppose by pulling the weights inward, the rotational inertia of the man reduces to half its value. By what factor would his rotational speed change?

double