Newton's 1st & 3rd Laws Flashcards
Newton’s 1st Law of Motion
Law of Inertia
Any object will remain at rest or moving with uniform motion (constant speed AND constant direction) iff the net force acting on that object is zero.
OR
A net force acting on an object will cause that object to accelerate (change its motion by changing its speed and/or direction).
a = f/m ⇒ responsiveness to force = net force/inertia
inertia
responsiveness of an object to force
inertia & mass
The measure of an object’s inertia is the object’s mass.
The more mass an object has, the more inertia it has, and the less it responds to force.
canceling a force
Only a force can resist/cancel another force. Mass(inertia) by itself cannot resist force.
When an obj appears to resist a force cuz it doesn’t accelerate in response 2 the force, always cuz another force is acting. usually friction.
Greek philosopher Aristotle asserted that
force is required for motion
heavier objects fall faster than lighter objects
the acceleration of an obj is due to
an unbalanced force acting on the object
An object following a striaght-line path at a constant velocity must
have zero acceleration
still forces, just canceled out
A moving truck is traveling down the road at constant velocity. Inside the storage compartment, a rock is dropped from the midpoint of the ceiling and strikes the floor below. The rock hits the floor
exactly below the midpoint of the ceiling
part of the system
same velocity
passenger in car moving in straight line at constant speed
car turns sharply to left and u’re thrown against side door
When a passenger is wearing a seatbelt, basically share the same state of motion as the car. accelerate and decelerate with car.
when not wearing seat belt, seaparte objects with separate rates of motion. when the car abruptly changes direction, the passenger continues with the same velocity as before (until they hit the door)
Newton’s 3rd Law of Motion
For every force there is an equal and opposite reaction force.
FAonB = -FBonA
action-reaction pair
the 2 forces involved
do not cancel each other
“equal”
equal in magnitude
occur @ exactly the same time & last for same amount of time - simultaneous
“opposite”
oppsoite in direction
180o
Why don’t action and reaction forces cancel each other out?
They are usually acting on different objects.
where do you draw vectors?
on the object receiving the force
Why does Bob meat Annie in tug of war?
Based on Newton’s 3rd Law, they are both exerting the same amount of force, but Bob still winds because he is exterting more force on the ground
If the floor is exerting a reaction force back on you due to your weight on it, then why don’t you get pushed into the air away from the floor?
Gravity pushes you down.
If a horse exerts a force on the cart & the cart exerts an equal but opp force on the horse, how can the horse move the cart?
There are more than just the 2 forces acting on the horse and cart.
Also, the 2 forces are both acting on different objects with different masses.
when can action-reaction forces cancel each other out?
if they are part of the same system and become internal forces
drawing tug of war vectors
rope on gm -> rope on gp <-
gm on rope <- gp on rope ->
earth on gm v gm on earth ^
earth on gp v gp on earth ^
ground on gm(ground helping gm) <- gm on ground ->
ground on gp -> gp on ground <-
ground on gm ^ gm on ground v
ground on gp ^ gp on ground v
