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Forces by Meghna Raman 621 (Newton's Second Law of Motion…
Forces
by Meghna Raman 621
Newton's First Law of Motion
state of motion doesn't change
if net force is 0
example
ball at rest remains at rest
until it is kicked
or force is applied
water rocket remains at rest
stays in launcher until released with force
until force is applied
objects at rest
stay at rest
objects in motion
stay in motion
law of inertia
tendency of an object to remain at rest
object at rest tends to remain at rest
Newton's Second Law of Motion
acceleration
net force/ mass
same direction as net force
example
more force when throwing a ball
more acceleration
10 N = 5kg * A
Acceleration = 2 m/s^2
net force
opposite direction of object's motion
N/kg = m/s^2
mass of rocket*acceleration
equals force of rocket
Newton's Third Law of Motion
one object exerts forces on another
second object exerts force on first object
Action and Reaction forces
don't cancel
don't act on same object
example
swimmer pushes against water
water pushes swimmer ahead
upward force of rocket
equals water coming from bottom
momentum
mass*velocity
kilo-meters per seconds
Work and Energy
Energy
kinetic
energy an object has
when in motion
example
kinetic energy of bird (0.1 kg)
going at 8 m/s
bird has less mass
so it has less kinetic energy
1/2
m
v^2
depends on mass and speed
energy of moving person
potential
example
stretching a rubber band
stores energy due to its position
stored energy
due to position or shape
energy is stored in the bow
potential energy = mgh
m = mass in kg
g= acceleration due to gravity
h = height in meters
elastic potential energy
when object is stretched or compressed
gravitational potential energy
energy is more when object is on a higher level
depends on mass, height, and acceleration due to gravity
ability to do work
joules
mechanical energy
sum of potential and kinetic energy
joules
newton-meter
Work
work = force * distance
2N*4m = 8 joules
joules
newtons per meter
direction object is moving = direction force is applied
