Transcript Forces and Newton*s Laws Quick Guide

Forces and
Newton’s Laws
Quick Guide
Forces
 Forces
are responsible for all
motion
 Forces cause change in motion,
or accelerations
Forces

Free body diagrams
 Represent
the forces acting on the object at
that moment.
 What
happened before, or may happen
next do not matter.
 Forces
vectors must be labelled (ex: the
accepted labels for gravitational force are
mg, FG, or W for weight).
 Vectors
should have lengths that correspond
to their values as they relate to one another.
Forces

Common forces include:
 Tension,
Normal
Applied, Gravitational, Friction,
 Remember
the normal is always
perpendicular to the surface.
 Net
force: sum of all forces acting on an
object. Must treat horizontal and vertical
forces independently. Net force is never
drawn on a FBD.
Newton’s Laws

First Law (Law of Inertia)
 Inertia
– tendency of an object to maintain
its motion
 An
object’s motion is unchanged unless
acted on by an unbalanced net force.
Newton’s Laws

Second Law
 An
object’s acceleration is dependent on the net
force acting on the object and the object’s mass.
F=ma
Σ𝐹
a =
𝑚
 A larger net force on the same mass will result in a
greater acceleration.
A
larger mass with the same net force will experience
a smaller acceleration.
Newton’s Laws

Third Law
 Force
 When
occur in action reaction pairs
objects interact they apply an equal
force in the opposite direction on one
another.
Newton’s Laws
 Third
Law Misconception
Forces are the SAME, it’s the
effect of the forces that is different
The sun and the Earth’s pull on
each other is EQUAL
Affects
the Earth more because the
earth has less inertia
Summary

Sketch a FBD for all situations involving force.

Keep horizontal and vertical forces independent.

Use the FBD to write force equations for horizontal
and vertical forces.

If the net force is 0, then the object is in equilibrium.
Force equations are set equal to 0.

If the net force is > 0, then the object has an
acceleration. Force equation is set equal to ma.