Download Chapter 6 Notes-Forces Types of Forces

Chapter 6 Notes-Forces
Great Scientists and their thoughts on Motion
Aristotle-old theory
Copernicus
Galileo-his theories are still used today
Force - A push or a pull on an object
The object or group of objects that get pushed or pulled is called the system.
The world around it that exerts the force is called the environment.
There are 2 groups of forces.
1. Contact Force-touching
Examples:
2. Long range force-exerted without contact
Examples:
Types of Forces
1. Friction Force-contact force that acts to oppose a sliding motion between
surfaces
2. Normal Force-Contact force exerted by a surface onto an object
3. Spring Force-Restoring Force, the push or pull a spring exerts on an
object
4. Tension Force-the pull exerted by a string, rope or cable when attached to
a body and pulled tight
5. Thrust Force-A general term for the forces that move objects such as
rockets, planes, cars and people
6. Weight Force-long range force due to gravitational attraction between 2
objects (generally the earth and a 2nd object)
Characteristics of Forces
Net forces will change the state of motion of an object
Can be exerted through long distances
Occur in Pairs
In each pair, each force works opposite of each other
Mass vs. Weight
The force called WEIGHT is a gravitational force.
Weight is not mass!!!
Mass-A measure of the amount of material in an object (it is not a force)
The mass of an object will be the same in any location.
Mass is measured in kilograms.
Weight-A measure of the gravitational force acting on an object
The weight of an object depends on its location and the amount of
gravitational pull at that location.
Weight is measure in Newtons.
W=Fg
A Newton is 1 kg*m/s2
F=mg
So, the force of an object measured in Newtons is equal to the mass of an object
times the amount of gravity acting on that mass.
Examples
1. The mass of an object is 23.2 kg and the amount of gravity acting on the
object is 9.8 m/s2. What is the Force of Weight of the object?
2. The force of weight of an object is -220 Newtons and the amount of gravity
pulling on the object is -9.8 m/s2. What is the mass of the object?
3. Determine Your Ideal Mass/Weight
You already know how much you “weigh” in pounds
Lets try to figure out your ideal weight on earth in kilograms and Newtons,
then on the moon.
1 kg = 2.2 lbs
There is 1/6 less gravity on the moon than on earth.
Vectors
Because forces have magnitude and direction, and can be combined with other
forces, we use VECTORS to draw forces.
Net Force-the combination of all the forces acting on an object.
Adding
Subtracting
Equilibrium
Objects move when a net force is applied to it.
It is the Net Force that changes an objects state of motion.
Adding Vectors
Subtracting Vectors
Remember, Forces are measured in Newtons because Isaac Newton came up
with the idea about forces.
He wrote 3 statements concerning forces-they are called Newton’s Laws of
Motion.
Newton’s First Law
“An object at rest tends to stay at rest and an object in motion tends to stay in
motion unless acted upon by an outside force”
Objects tend to keep doing what they are doing.
Forces that have an influence on this law are friction and intertia.
The Net Force changes the velocity of an object. So, something will keep doing
what it is doing unless some Net Force acts on it.
Newton’s Second Law
“The acceleration produced by a net force on an object is directly proportional
to the magnitude of the net force, is in the same direction as the net force, and is
inversely proportional to the mass of the object”
The combination of forces acting on an object is the net force.
Acceleration depends on the net force.
To increase the acceleration of an object you must increase the net force acting
on it.
So, the acceleration is directly proportional to the net force.
Acceleration depends on the mass being pushed or pulled. They are inversely
proportional to each other.