# second semester physics

## Terms

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position
location of an object
distance
space between two places
speed
how fast an object is moving (rate of change of position)
constant speed
doesn't change
average speed
total distance divided by total time
instantaneous speed
at the moment
velocity
how fast and what direction object is moving
average speed formula
v= d/t
what is the speed of a truck that travels 15 miles in 20 minutes? (in mph)
v= ?
d= 15 miles
t= 20 minutes

t=20 min x 1hr/60 min = .33 hrs

15 mi/.33 hrs = 45 mph
reference point
frame of reference
"with respect to..."
***usually the earth***
acceleration
rate of change of velocity
acceleration formula
a= final velocity - initial velocity
---------------------------------
time
from rest a bike accelerates to 12 m/s in 25 s. what is the rate of acceleration?
inital v= 0 m/s
final v= 12 m/s
t= 25 s
a=?

a= 12 m/s - 0 m/s
--------------
25 s

a= .48 m/s2
unit for acceleration
miles per second squared

m/s2
unit for distance
meters
m
unit for velocity
miles per second
m/s
unit for time
seconds
s
what are the positive and negative accelerations
faster, starting --> positve

slower, stopping, turning --> negative
inertia
objects resistance to changes in motion
force
push or pull that one object exerts on another
what can change the velocity of an object?
force
balanced forces
cancel each other out
same size
moving in opposite directions
**sum of all forces acting on object = 0 net force
unbalanced forces
net force doesn't equal zero
cause acceleration
Newton's 1st Law of Motion
"Law of Inertia"
-objects at rest stay at rest, objects in motion stay in moving in a straight line at a constant speed unless action on by an unbalanced forced
gravity
-force of attraction between two objects in the universe
-depends on mass and distance between them
properties of gravity
bigger the mass, bigger force of gravity

bigger the distance, smaller force of gravity
friction
force that opposes motion
-sliding
-rolling
-fluid (liquid/gas...air resistance)
Newton's 2nd Law of Motion
-acceleration of an object increases as the net force on that object increases
-force increases, acceleration increases
-mass increases, acceleration decreases
(force is proportional to acceleration)
force formula
force= mass x acceleration

f= m x a
unit for force
kg x m/s2 ----> NEWTON
max acceleration of a fist in a karate blow is 3500 m/s2. if the fist has a mass of .70 kg, how much force can the fist exert?
F= ?
m= .70 kg
a= 3500 m/s2

F= .70 kg x 3500 m/s2

F= 2450 N
weight
-doesn't equal mass
-force of gravity between object and large body (planet)
-depends on location
-measured w/ scale and Newtons
mass
-amount of matter
-measured in kilograms
-constant everywhere
weight formula
weight= mass x gravity

W= m x g
acceleration due to gravity
9.8 m/s2
unit for weight
Newton
unit for gravity
m/s2
what is the mass of a 400 N rock?
m=?
W= 400 N
g= 9.8 m/s2

400 N= m x 9.8m/s
----- ------
9.8m/s2 9.8m/s2

m= 40.8 kg
falling objects
(neglect air resistance)
everything falls at same rate of acceleration on earth (9.8 m/s2)
falling objects
(w/ air resistance)
-fluid friction= force that opposes motin
-depends on size, shape, speed (more speed, more air resistance)
-eventually force of gravity equals air resistance (terminal velocity)
falling objects formula
distance = 1/2 gravity x time squared

d= 1/2gt2
projectile motion
-horizontal throwing
v= d/t
projectile motion
-dropping something
a= final velocity - initial velocity
--------------------------------
time

or

d= 1/2gt2
Newton's 3rd Law of Motion
-forces always come in pairs (Action-Reaction Pair)
-when an object exerts a force on another object, then the 2nd object exerts the same size force in the opposite direction on the first object
centripetal force
-causes circular motion
-always directed towards center of circle
centrifugal force
no such thing
centripetal acceleration
acceleration towards the center of a circular path
momentum formula
momentum= mass x velocity
p=m x v
law of conversation of momentum
momentum before a collision is equal to momentum after a collision
work
force applied over a distance in the same direction
work formula
Work= force x distance
power
how fast work is done
power formula
power= work
----
time
unit for work
joule
unit for power
watt
1 hp= ?
550 ft-lb
----
s
and

746 watts
energy
ability to do work or to create a change in itself or its surroundings
5 types of energy
mechanical
chemical
electromagnetic
thermal
nuclear
kinetic energy
energy in form of motion of object
kinetic energy formula
KE = 1/2mv2
potential energy
energy due to objects position/condition (edge/stretched)
potential energy formula
PE= m x g x h
units for kinetic and potential energy
joule

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