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Forces & Newton’s LawsForces & Newton’s Laws
Chapter 11 NotesChapter 11 Notes
ForcesForces
A force is a push or pull exerted on an object
Forces tend to change the motion of an object
A force has two components Magnitude (how much) Direction (which way)
A force is a push or pull exerted on an object
Forces tend to change the motion of an object
A force has two components Magnitude (how much) Direction (which way)
Mass vs WeightMass vs Weight
Many confuse the difference between mass and weight Mass = How much matter an object has
Measured typically in grams (or kg) Weight = Gravitation pull on an object
Weight = mass * gravitational acceleration
Many confuse the difference between mass and weight Mass = How much matter an object has
Measured typically in grams (or kg) Weight = Gravitation pull on an object
Weight = mass * gravitational acceleration
Mass vs Weight Mass vs Weight Take an object of mass 100 kg
On earth the mass = 100 kg On the moon the mass - 100 kg In outer space the mass = 100 kg
Weight of same object On Earth the weight = 980 N On the moon the weight = 160 N In outer space the weight = 0 N
Take an object of mass 100 kg On earth the mass = 100 kg On the moon the mass - 100 kg In outer space the mass = 100 kg
Weight of same object On Earth the weight = 980 N On the moon the weight = 160 N In outer space the weight = 0 N
Unit of ForcesUnit of Forces
There are several units that can be used to measure force Many of you are most familiar with the unit of pound (lb)
The metric unit for force (the one we will use) is the Newton (N)
There are several units that can be used to measure force Many of you are most familiar with the unit of pound (lb)
The metric unit for force (the one we will use) is the Newton (N)
Unit of Force Unit of Force
What is a Newton?
It is a derived unit
It is an abbreviation for:
(Kg * m ) / s2
What is a Newton?
It is a derived unit
It is an abbreviation for:
(Kg * m ) / s2
Net ForceNet Force
Net forces are more important than individual forces
A net force of the sum total of all the individual forces acting on an object
Net force is written as: ∑F
Net forces are more important than individual forces
A net force of the sum total of all the individual forces acting on an object
Net force is written as: ∑F
Net ForceNet Force
If the net force is zero the forces are considered to be BALANCED
If the net force is NOT zero the forces are considered to be UNBALANCED
If the net force is zero the forces are considered to be BALANCED
If the net force is NOT zero the forces are considered to be UNBALANCED
Balanced vs UnbalancedBalanced vs Unbalanced
When forces are BALANCED the motion of an object will remain constant
When forces are UNBALANCED the motion of an object will change…….it will ACCELERATE
When forces are BALANCED the motion of an object will remain constant
When forces are UNBALANCED the motion of an object will change…….it will ACCELERATE
Net ForceNet Force
Example: Find the net force if a 300 N force acts to the right and a 120 N force acts to the left
Example: Find the net force if a 300 N force acts to the right and a 120 N force acts to the left
Net ForceNet Force
Example: Find the net force if a 400 N force acts to the right, a 120 N force acts to the left, and a 75 N forces acts to the left
Example: Find the net force if a 400 N force acts to the right, a 120 N force acts to the left, and a 75 N forces acts to the left
FrictionFriction
Friction is a force that opposes motion It occurs when two surfaces are in contact
It depends on: The weight of the object The type of surfaces
Friction always slows down an object
Friction is a force that opposes motion It occurs when two surfaces are in contact
It depends on: The weight of the object The type of surfaces
Friction always slows down an object
Types of FrictionTypes of Friction
Static friction Occurs when the surfaces in contact do NOT slide past one another
Kinetic friction Occurs when the surfaces in contact slide past one another
Static friction Occurs when the surfaces in contact do NOT slide past one another
Kinetic friction Occurs when the surfaces in contact slide past one another
Kinetic FrictionKinetic Friction
Kinetic friction is often referred to as sliding friction
If a round object rolls over a flat surface it is often referred to as rolling friction
Kinetic friction is often referred to as sliding friction
If a round object rolls over a flat surface it is often referred to as rolling friction
Types of FrictionTypes of Friction
Static friction is always greater than kinetic/rolling friction
Rolling friction is typically less than sliding friction
Static > Sliding > Rolling
Static friction is always greater than kinetic/rolling friction
Rolling friction is typically less than sliding friction
Static > Sliding > Rolling
DragDrag
Any object that moves through a fluid (like air) experiences a frictional force called air resistance
Another term for air resistance is DRAG
Any object that moves through a fluid (like air) experiences a frictional force called air resistance
Another term for air resistance is DRAG
FrictionFriction
Can be harmful Engine parts Air resistance
Can be helpful Warming your hands Starting/Stopping/Turning Brillo pads
Can be harmful Engine parts Air resistance
Can be helpful Warming your hands Starting/Stopping/Turning Brillo pads
Newton’s LawsNewton’s Laws
Sir Isaac Newton(1643-1727)
Developed Laws ofmotion
Sir Isaac Newton(1643-1727)
Developed Laws ofmotion
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Newton’s LawsNewton’s Laws
Newton was a student on break when he started to form his thoughts on motion
He challenged the belief system in regard to motion that had been establish over 2000 years ago
Newton was a student on break when he started to form his thoughts on motion
He challenged the belief system in regard to motion that had been establish over 2000 years ago
Newton’s LawsNewton’s Laws
He summarized his thoughts into three Laws of Motion Law of Inertia F = ma Action/Reaction Pairs
He summarized his thoughts into three Laws of Motion Law of Inertia F = ma Action/Reaction Pairs
Newton’s 1st LawNewton’s 1st Law
An object at rest will stay at rest OR an object in motion will stay in motion UNLESS a NET force acts on the object
An object at rest will stay at rest OR an object in motion will stay in motion UNLESS a NET force acts on the object
Newton’s 1st LawNewton’s 1st Law
Often referred to as the Law of Inertia
What is Inertia? property of matter tendency of an object to resist changes in motion
more mass = more inertia
Often referred to as the Law of Inertia
What is Inertia? property of matter tendency of an object to resist changes in motion
more mass = more inertia
Newton’s 2nd LawNewton’s 2nd Law
A net force acting on an object will cause the object to change its motion - it will accelerate
The magnitude of the force and the mass of the object will both influence the acceleration
A net force acting on an object will cause the object to change its motion - it will accelerate
The magnitude of the force and the mass of the object will both influence the acceleration
Newton’s 2nd LawNewton’s 2nd Law
Written as an equation
∑ F = m a
Written as an equation
∑ F = m a
Newton’s 3rd LawNewton’s 3rd Law
For every force there is an EQUAL but OPPOSITE reaction force
Examples Baseball - Bat Bug - Windshield
For every force there is an EQUAL but OPPOSITE reaction force
Examples Baseball - Bat Bug - Windshield