2nd: Acceleration is produced by a net force on an object and is directly proportional to the magnitude of the force, in the same direction as the force, and is inversely proportional to the mass of the object.
acceleration proportional to net force
2 pple pushing car
acceleration prop 1 / mass
pushing a bike vs a car
$$\Sigma F=ma$$
Friction force increases to opposing force?
there is a maximum friction force
not depend on speed, only surface
does not matter on surface of contact
Depends on roughness
more weight == greater support force → more friction
Types of Friction
Static Friction
cancelling applied force at rest
Kinetic friction
static friction > kinetic
acted on a moving object
mass vs weight
Mass == amount of matter (gram)
Weight is force of gravity (Newton)
Weight is 0 on moon because there is no gravity on the moon
mass is the same in the moon as in earth
pull by gravity == gravitational force == weight
This accelerate when falling (gravitational acceleration)
free fall is accelerating 10m/s/s
gallelio gravity experiment
things fall at a constant acceleration
dropping a bowling ball and a tennis ball, both will hit at same time
3rd: Every reaction has an equal and opposite reaction.