4.1: Force #

4.2: Newton’s First Law of Motion #

Galileo imagined an idealealized world → one without friction
With this in mind, Galileo realized that without force on a moving object, it will continue to move with constant speed in a straight line
This idea leads into Newton’s 1st Law
- Every object continues in its state of rest, or of uniform velocity in a staight line, as long as no net force acts on it.
- the tendency of an object to maintain its state of rest or of uniform velocity in a straight line is called inertia
inertial reference frames are frames in which Newton’s 1st law holds (constant velocity / non-accelerating frames)

in physics, mass is the measure of inertia → the more mass an object has, the greater force required to give it an acceleration
mass is not weight
- mass is a property (its quantity of matter)
- weight is a force, the pull of gravity acting on an object

Net force causes acceleration
- consider how one would push a cart and how that would affect acceleration and time
the acceleration of an object is directly proportional to the net force acting on it, and is inversely proportional to the object’s mass. The direction of the acceleration is in the direction of net force acting on the object

math equations from txtbook

intuitive, but, the component of acceleration in each direction is affected only the component ot the net force in that direction
++ // eqs
given defintion of mass as inertia, acceleration or mass of 2 objects with equal force can be found via m1/m2 = a1/a2

formal definition: whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first