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Mass Weight and Free Fall Notes
Newton’s Laws
Newton’s First law – The Law of Inertia
Every object continues in a state of rest, or in a state of motion in a
straight line unless acted upon by an unbalanced force.
“objects at rest stay at rest, objects in motion stay in motion, unless acted
upon by a force”
Net force – a combination of all of the forces acting on an object
Newtons – scientific unit for force
Representing forces
Forces are vectors that can be represented using arrows showing direction and
magnitude (how much)
Equilibrium for forces at rest (Static equilibrium)
When equal but opposite forces are acting on something it is in equilibrium
ΣF=0
Σ= vector sum of
F= force
Direction important – example: if up force is (+) then the down force is (-)
Example pg 26-27
Support forces – upward supporting force
Book at rest on a desk
Forces = gravity or weight (-), desk (+) (support force)
Equilibrium for moving objects (Dynamic equilibrium)
Object at rest =equilibrium
Object moving at a constant speed in the same direction = equilibrium
3.3 Mass is a measure of inertia
Mass – the amount of matter in an object. Also, a measure of inertia, or resistance
to changes in motion. (Same on every planet)
Weight – is the force due to gravity that acts on an object’s mass (different on
every planet due to differences in gravity)
Mass and weight are proportional to each other
1 kilogram = 9.8 newtons exactly (For in class calculation use 9.8 newtons)
10 newtons = the force of gravity
Free fall
Vf = g x t g = acceleration due to gravity or 10 m /sec/sec t = time
D = ½ g x t2 d = distance
Pg 32 exercises #8-19
Newton’s second law
Acceleration produced by a net force on an object is directly proportional
to the net force, is in the same direction, and is inversely proportional to
the mass of the object.
a= F/m a=acceleration
F=force
m=mass
Friction is a force that affects motion
Objects in Free Fall –
Large mass = large affect of force of gravity = same acceleration = small mass =
small affect of force of gravity
Terminal velocity – maximum speed air resistance (+) equals force of gravity (-) and net
forces = 0 which mean 0 acceleration
Newton’s third law –
Whenever one object exerts a force on a second object, the second object exerts
an equal and opposite force on the first. “for every action there is an equal and
opposite reaction”
Ex. Tire pushed on road, road pushes on tire