Newton’s LawsNewton’s Laws

Unit 2Unit 2

Contributors to the theory of Contributors to the theory of motionmotion

AristotleAristotle

Divided motion into two types: Divided motion into two types: natural and violentnatural and violent

Natural motion- either straight up or Natural motion- either straight up or straight downstraight down

Violent motion- the result of forces Violent motion- the result of forces that pushed or pulledthat pushed or pulled

CopernicusCopernicus

Reasoned that the Earth moved Reasoned that the Earth moved around the sunaround the sun

GalileoGalileoSupported CopernicusSupported CopernicusForce: any push or pullForce: any push or pullFriction: force that acts between Friction: force that acts between materials that touch as the move materials that touch as the move past each otherpast each otherArgued that only when friction is Argued that only when friction is present is a force needed to keep an present is a force needed to keep an object movingobject movingInertia: the property of a body to Inertia: the property of a body to resist changeresist change

NewtonNewton

Developed the famous laws of Developed the famous laws of motionmotion

Newton’s First LawNewton’s First Law

Law of Inertia:Law of Inertia:Every object continues in a Every object continues in a

state of rest, or of motion in a state of rest, or of motion in a straight line at constant straight line at constant

speed, unless it is compelled speed, unless it is compelled to change that state by forces to change that state by forces

exerted upon it.exerted upon it.

The more mass an object has, the greater The more mass an object has, the greater its inertia & the more force it takes to change its inertia & the more force it takes to change

its state of motionits state of motion

Mass is different than volume & Mass is different than volume & weight.weight.

mass: a measure of the inertia an mass: a measure of the inertia an object hasobject has

Volume: a measure of spaceVolume: a measure of space

Weight: the force of gravity on an Weight: the force of gravity on an objectobject

weight= mass x gravityweight= mass x gravity

The combination of all forces acting on The combination of all forces acting on an object is called the net force.an object is called the net force.

It is the net force that changes an It is the net force that changes an object’s state of motion.object’s state of motion.

When an object is at rest, forces balance & When an object is at rest, forces balance & produce a net force of zero. One force is produce a net force of zero. One force is

gravity. The other force is the normal force. gravity. The other force is the normal force. This means that the object is in a state of This means that the object is in a state of

equilibrium.equilibrium.

Felicia, a ballet dancer, has a mass Felicia, a ballet dancer, has a mass of 45kg. of 45kg.

What is Felicia’s weight on Earth?What is Felicia’s weight on Earth?

What is Felicia’s mass on Jupiter, What is Felicia’s mass on Jupiter, where the acceleration due to where the acceleration due to

gravity is 25 m/sgravity is 25 m/s22??

What is Felicia’s weight on Jupiter?What is Felicia’s weight on Jupiter?

A 20g sparrow flying toward a A 20g sparrow flying toward a bird feeder mistakes the pane of bird feeder mistakes the pane of

glass in a window for an glass in a window for an opening and slams into it with a opening and slams into it with a force of 2N. What is the bird’s force of 2N. What is the bird’s

acceleration?acceleration?

A 30g arrow is shot by William A 30g arrow is shot by William Tell through an 8cm thick apple Tell through an 8cm thick apple sitting on top of his son’s head. sitting on top of his son’s head. If the arrow enters the apple at If the arrow enters the apple at 30m/s and emerges at 25m/s in 30m/s and emerges at 25m/s in

the same direction, with what the same direction, with what force has the apple resisted the force has the apple resisted the

arrow?arrow?

Newton’s Second LawNewton’s Second Law

Force = mass x accelerationForce = mass x acceleration

Force causes acceleration.Force causes acceleration.

To increases the acceleration of an To increases the acceleration of an object, you must increase the net object, you must increase the net

force acting on it.force acting on it.

The acceleration depends on the The acceleration depends on the mass.mass.

Acceleration is inversely Acceleration is inversely proportional to the mass.proportional to the mass.

Force= mass x accelerationForce= mass x acceleration

Friction acts on materials that are in contact Friction acts on materials that are in contact with each other. It always acts in a direction with each other. It always acts in a direction

to oppose motion. The force of friction to oppose motion. The force of friction between surfaces depends on the kinds of between surfaces depends on the kinds of

materials in contact & how much the materials in contact & how much the surfaces are pressed together.surfaces are pressed together.

Friction also occurs in liquids & gases. Fluid Friction also occurs in liquids & gases. Fluid friction occurs as an object pushes aside the fluid it friction occurs as an object pushes aside the fluid it

is moving through. An example is air resistance.is moving through. An example is air resistance.

When friction is present, an object may move with When friction is present, an object may move with a constant velocity even when an outside force is a constant velocity even when an outside force is applied to it. The friction force just balances the applied to it. The friction force just balances the

applied force so the net force is zero and no applied force so the net force is zero and no acceleration occurs.acceleration occurs.

Pressure= force/ area of applicationPressure= force/ area of application

The smaller the area supporting a The smaller the area supporting a given force, the greater the pressure given force, the greater the pressure on that surface.on that surface.

Measured in pascals (Pa)Measured in pascals (Pa)

One Newton per square meter equals One Newton per square meter equals one pascalone pascal

Galileo showed that objects in Galileo showed that objects in free fall accelerate equally free fall accelerate equally regardless of their masses.regardless of their masses.

A 10kg cannonball and a 1kg A 10kg cannonball and a 1kg rock would fall with equal rock would fall with equal

accelerations- 10 m/s.accelerations- 10 m/s.

When air resistance is present, a falling object accelerates When air resistance is present, a falling object accelerates only until it reaches its terminal speed. At terminal speed, only until it reaches its terminal speed. At terminal speed, the force of air resistance balances the force of gravity & the force of air resistance balances the force of gravity &

the net force is zerothe net force is zeroAcceleration= weight - resistanceAcceleration= weight - resistance

Rose is sledding down an ice-Rose is sledding down an ice-covered hill inclined at an angle covered hill inclined at an angle of 15 degrees to the horizontal. of 15 degrees to the horizontal.

If Rose and the sled have a If Rose and the sled have a combined mass of 54kg, what is combined mass of 54kg, what is the force pulling them down the the force pulling them down the

hill?hill?

Brian is walking through the school Brian is walking through the school cafeteria but does not realize that cafeteria but does not realize that the person in front of him has just the person in front of him has just spilled his glass of chocolate milk. spilled his glass of chocolate milk. As Brian, who weighs 420N, steps As Brian, who weighs 420N, steps in the milk, the coefficient of sliding in the milk, the coefficient of sliding friction between Brian and the floor friction between Brian and the floor is suddenly reduced to 0.040. What is suddenly reduced to 0.040. What

is the force of sliding friction is the force of sliding friction between Brian and the slippery between Brian and the slippery

floor?floor?

While redecorating her apartment, While redecorating her apartment, Kitty slowly pushes an 82kg china Kitty slowly pushes an 82kg china cabinet across the wooden dining cabinet across the wooden dining

room floor, which resists the motion room floor, which resists the motion with a force of friction of 320N. with a force of friction of 320N. What is the coefficient of sliding What is the coefficient of sliding

friction between the china cabinet friction between the china cabinet and the floor?and the floor?

At Sea World, a 900kg polar bear At Sea World, a 900kg polar bear slides down a wet slide inclined at slides down a wet slide inclined at

an angle of 25 degrees to the an angle of 25 degrees to the horizontal. The coefficient of friction horizontal. The coefficient of friction between the bear and the slide is between the bear and the slide is

0.0500. What frictional force 0.0500. What frictional force impedes the bear’s motion down impedes the bear’s motion down

the slide?the slide?

Newton’s Third LawNewton’s Third Law

Whenever one object exerts a force on a Whenever one object exerts a force on a second object, the second object exerts second object, the second object exerts an equal and opposite force on the first an equal and opposite force on the first

object.object.

Newton realized that a force is not a Newton realized that a force is not a thing in itself but part of a mutual thing in itself but part of a mutual

action, an interaction, between one action, an interaction, between one thing & another.thing & another.

In every interaction, the forces always In every interaction, the forces always occur in pairs & cannot exist without occur in pairs & cannot exist without

each other.each other.

One force is called the action force. One force is called the action force. The other is called the reaction force.The other is called the reaction force.

Action: Object A exerts a force on Object BAction: Object A exerts a force on Object B

Reaction: Object B exerts a force on Object AReaction: Object B exerts a force on Object A

Remember that action-reaction force pairs Remember that action-reaction force pairs are equal but opposite in strength. We must are equal but opposite in strength. We must also take mass into account. A given force also take mass into account. A given force

exerted on a small mass produces a greater exerted on a small mass produces a greater acceleration than the same force exerted on acceleration than the same force exerted on

a large mass.a large mass.

Newton’s Third law helps us to Newton’s Third law helps us to explain how rockets are explain how rockets are

propelled, how helicopters get propelled, how helicopters get their lifting force, and how birds their lifting force, and how birds

and airplanes fly.and airplanes fly.

Since action and reaction forces Since action and reaction forces are equal but opposite, why are equal but opposite, why don’t they cancel to zero?don’t they cancel to zero?

If action & reaction forces are internal to a system, If action & reaction forces are internal to a system, they cancel each other & produce no acceleration they cancel each other & produce no acceleration

of the system. A force external to the system is of the system. A force external to the system is needed to accelerate the system.needed to accelerate the system.

Flip, an exhausted gymnast, Flip, an exhausted gymnast, hangs from a bar by both arms hangs from a bar by both arms

in an effort to catch his breath. If in an effort to catch his breath. If Flip has a mass of 65kg, what is Flip has a mass of 65kg, what is

the tension in each of Flip’s the tension in each of Flip’s arms as he hangs in place?arms as he hangs in place?

At an art auction, Whitney has At an art auction, Whitney has acquired a painting that now acquired a painting that now

hangs from a nail on her wall. If hangs from a nail on her wall. If the painting has a mass of the painting has a mass of

12.6kg, what is the tension in 12.6kg, what is the tension in each side of the wire supporting each side of the wire supporting

the painting?the painting?

Michelle likes to swing on a tire tied Michelle likes to swing on a tire tied to a tree branch in her yard. If to a tree branch in her yard. If Michelle and the tire have a Michelle and the tire have a

combined mass of 82.5kg, and combined mass of 82.5kg, and Elwin pulls Michelle back far Elwin pulls Michelle back far

enough for her to make an angle to enough for her to make an angle to 30 degrees with the vertical, what is 30 degrees with the vertical, what is the tension in the rope supporting the tension in the rope supporting

Michelle and the tire?Michelle and the tire?

After returning home from the After returning home from the beach, Samantha hangs her beach, Samantha hangs her wet 0.20kg bathing suit in the wet 0.20kg bathing suit in the

center of the 6m long center of the 6m long clothesline to dry. This causes clothesline to dry. This causes

the clothesline to sag 4cm. the clothesline to sag 4cm. What is the tension in the What is the tension in the

clothesline?clothesline?

Brooke comes home from Brooke comes home from school and puts her books down school and puts her books down

on the kitchen table while she on the kitchen table while she goes to grab a snack. The goes to grab a snack. The

books have a combined weight books have a combined weight of 25N and the area of contact of 25N and the area of contact

is 0.19m by 0.24m. What is 0.19m by 0.24m. What pressure do the books apply on pressure do the books apply on

the table?the table?

A full coffee mug has a mass of A full coffee mug has a mass of 0.6kg and an empty mug has a 0.6kg and an empty mug has a mass of 0.3kg. If the full mug mass of 0.3kg. If the full mug

applies a pressure of 1200Pa, what applies a pressure of 1200Pa, what is the area inside a circular ring of is the area inside a circular ring of

coffee left on the table by the coffee left on the table by the bottom of the mug?bottom of the mug?

What is the radius of the ring of What is the radius of the ring of coffee?coffee?