Transcript Forces and Newton`s Laws

Forces
May they be with you 
What is a force?
A force is defined as the push or
pull on an object.
Forces
• Some common types of force
– Fg = force of gravity
– Ff = force of friction
– Ft = force of tension
– Fn = normal force
– Fa = applied force
– Fnet = sum of all forces
What are the different
types of forces?
1. GRAVITY – is a force
that pulls down on objects
Fg
What are the different
types of forces?
2. NORMAL– is the force
a surface “pushes” into
an object
FN
• If the surface is flat, normal
force pushes straight up. (90°)
Fg
Fg
FN
• If the surface is angled, the normal
force “looks” angled. (but is 90° to the
surface)
What are the different
types of forces?
3. FRICTION– is a force that
appears whenever two things are in
contact.
• No matter which direction
• something moves in,
• friction pulls it the other way.
What are the different
types of forces?
4. TENSION– is a pulling force
exerted by a string, cable, chain,
or rod on another object.
• Tension is the opposite of
compression.
What are the different types
of forces?
5. COMPRESSION– a pushing
force exerted on another
object. for ex; spring
FC
HOW FORCES “BEHAVE”
Forces follow three
basic laws called
Newton's laws
Newton’s Laws of Motion
1st Law of Motion
An object at rest will stay at
rest unless acted on.
An object in motion will stay
in motion unless acted on.
1st Law of Motion
• “objects will stay doing what they are doing”
• The tendency of an object to resist a change in
their motion is called Inertia
• The more mass an object has the more inertia it
has
2nd Law of Motion
Force is equal to mass
times acceleration
2nd Law of Motion
• F=ma
• The acceleration of an object depends
on the net force acting on an object.
• Net force = the addition of all the
forces acting on an object
3rd Law of Motion
For every action there is an
opposite and equal reaction
Mass vs. Weight
• Mass – how much matter is in something
• Weight – how much something is pulled
by gravity. Depends on where you are
located
Force of Friction
• Occurs when two objects are in
contact with each other.
• Coefficient of friction (μ – mu)
– μ= friction force/weight
• The coefficient of friction depends on whether
the object is sliding or not.
– If the object is sliding μ is slightly less
– This is called sliding or kinetic friction
– When friction holds an object at rest we call it
static friction.