Mass vs. Weight

Newton’s First Law of Motion INERTIA is the tendency of an object to resist changes in their state of motion. Mass is a measure of inertia. Object with small mass -----> has less inertia Object with large mass --------> has more inertia Ex: Imagine how difficult playing softball with a bowling ball. Hard to pitch Hard to change its direction

What is mass?

Mass is the measure of the inertia of an object The more mass an object has, the harder it is to move it (or stop it) Mass ≠ Weight Weight changes due to gravity You can be “weight-less” in space...but you’re not mass-less! Mass

Newton’s First Law of Motion MASS is a measure of the amount of matter in an object Mass will not change as you move from place to place WEIGHT is a measure of the gravitational force exerted on an object (the force with which Earth’s gravity pulls on a quantity of matter) The force varies from place to place Ex: Weight of an object will be different on Earth than on the moon

Mass, Continued Mass is a PROPERTY Weight is a FORCE Measured in kilograms (kg) Weight is a FORCE Measured in newtons (N) A force, in simple terms, is either a push or a pull

(Pushing a Car) Would pushing a car be any easier on the moon? No! The car has the same mass, even if the weight is lighter

Review Newton’s First Law of Motion

Review

Net Force: Force: An action exerted on an object (a push or a pull) in order to change the state of rest or motion of an object. Measured in Newtons (N) Net Force: Combination of all the forces acting on an object. (add them up)

Two teams that are evenly matched play tug-o-war NOTHING HAPPENS Balanced Forces If all of the pushes and pulls are even on an object, then the object “keeps on doing what it was doing” Tug-o-war Two teams that are evenly matched play tug-o-war NOTHING HAPPENS

Balanced Forces when net force is zero Does not cause a change in object’s motion

Unbalanced forces cause objects to change velocities Tug-o-war Two teams that are unevenly matched play tug-o-war One team will win

Unbalanced Force What happens when an object has an unbalanced force acted upon it? Unbalance forces cause acceleration!!

If the forces are… Equal – Unequal – Nothing happens Ex: A book sitting on a shelf Fg = 25 N FN = 25 N Unequal – The object changes what it is doing Ex: FA = 25 N right FA = 100 N left

F = mass x acceleration F = m a Newton’s 2nd Law The acceleration of an object is directly proportional to the net force acting on the object and is inversely proportional to the mass of the object. In other words: F = mass x acceleration F = m a

F = m*a m Fg g m “Weight” g