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