Define the following termsA. WeightB. GravityC. Friction

S-24I can explain the relationship between weight, gravity, and friction

What does friction normally do to a moving object?

What would be different in the world if there was not friction?

S-25I can describe different kinds of force.

SPS8 Students will determine relationships among force, mass, and motion.

b. Apply Newton’s three Laws to everyday situations.

c. Relate falling objects to gravitational force.d. Explain the difference in mass and weight.

Chapter 12Newton’s Laws

How do forces affect the motion of an object?What the four main types of friction?How do gravity and air resistance affect a falling object?In what direction does Earth’s gravity act?

12.1 Forces

Force – a push or a pull on an objectForces cause changes in velocity

Acceleration - change the objects speed or direction

Measured Scale, Force Sensor

Unit – measured in Newton’s (N) A medium apple will apply a force

of about 1 N

12.1 Force12.1 ForcesHow do forces affect the motion of an object?

Forces are vectors so they are drawn using arrows (show magnitude and direction)

Net Force – the overall force acting on an object after all the forces are combined Balanced forces – the net force is zero,

no acceleration Unbalanced forces – objects accelerate

12.1 Force12.1 ForcesHow do forces affect the motion of an object?

Friction – a force that opposes the motion of objects that touch as they move past each other

Four Types Static Friction – when objects aren’t

moving Sliding Friction – when objects are sliding

past each other

12.1 Force12.1 ForcesWhat are the four main types of friction

Rolling Friction – allows movement forward, but not side to side

Fluid Friction – when an object is moving through a fluid

▪ Fluids are liquids or gases – anything that flows

▪ Air resistance is a form of fluid friction

12.1 Force12.1 ForcesWhat are the four main types of friction

Gravity – the force of attraction between any two objects with mass Earth’s gravity points toward the center

of the earth – pulls anything with mass Called weight

12.1 Force12.1 ForcesHow does gravity and air resistance affect a falling object

When an object is falling, two forces act on it

What do you think they are?▪ Weight▪ Air Resistance

Objects will accelerate because of gravity until they reach a terminal velocity – the speed at which the weight and air resistance are equal

For example – terminal speed of a raindrop is about

9 m/s Human – 76 m/s

12.1 Force12.1 ForcesHow does gravity and air resistance affect a falling object

Gravity (Weight)

AirResistance

Name and describe the four types of friction.

S-26I can describe different kinds of force.

What is the difference between weight and mass.

S-27I can describe different kinds of force.

How does Newton’s first law relate change in motion to a zero net force?How does Newton’s second law relate force, mass, and acceleration?How are weight and mass related?

12.2 Newton’s 1st and 2nd Laws of Motion

12.1 Force12.2 Newton’s 1st & 2nd LawsHow does Newton’s first law relate change in motion to a zero net force Newton’s First Law of Motion

The state of motion of an object does not change as long as the net force acting on the object is zero

More commonly▪ An object at rest remains at rest, and an

object in motion remains in motion, unless acted on by an outside force.

Sometimes called the law of inertia▪ Inertia – the tendency of an object to

resist a change in its motion

12.1 Force12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion

The acceleration of an object is equal to the net force acting on it divided by the object’s mass.

F – Force in Newtons m – mass in kilograms a – acceleration in m/s2

Always in the same direction as the net force

F ma

12.1 Force12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –

Practice Problems A car with a mass of 1000 kg

accelerates when the traffic light turns green. If the net force on the car is 4000 N, what is the cars acceleration?Equation?Variables?Filled In Equation?Answer?

F ma

m 1000 kgF 4000N

4000N 1000 kgb c

aa 4 m s2-

12.1 Force12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –

Practice Problems An automobile with a mass of 1200

kg accelerates at a rate of 3.0 m/s2. What is the force acting on the automobile?Equation?Variables?Filled In Equation?Answer?

F ma

m 1200 kg

a 3.0 m s2-

F 1200 kgb c

3.0 ms2ffffff

d eF 400N

12.1 Force12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –

Practice Problems A 25 N force accelerates a man on a

scooter at 0.5 m/s2. What is the mass of the man and scooter?Equation?Variables?Filled In Equation?Answer?

F ma

F 25Na 0.5 m s2

-

25N m 0.5 ms2ffffff

d em 50 kg

12.1 Force12.2 Newton’s 1st & 2nd LawsHow are weight and mass related Weight and Mass

Weight the force of gravity acting on an object

Its mass times acceleration due to gravity

W – Weight in Newtons m – mass in kilograms g – 9.80 m/s2

Wmg

12.1 Force12.2 Newton’s 1st & 2nd LawsHow are weight and mass related Weight and Mass

Mass is a measurement of the inertia of an object

Weight is a measurement of the force of gravity acting on an object

What is Newton’s third law of motion?

12.3 Newton’s 3rd Law of Motion and Momentum

12.1 Force12.3 Newton’s 3rd LawWhat is Newton’s third law of motion

Newton’s Third Law Whenever one object exerts a force on a

second object, the second object exerts an equal and opposite force on the first object.

Identify the following action and reaction forces

12.1 Force12.3 Newton’s 3rd LawWhat is Newton’s third law of motion

Newton’s Third Law Action-Reaction pairs can cause motion

The donkey pushes on the ground, the ground pushes the donkey forward

Does the donkey push the ground backward?

Action-Reaction pairs don’t cancel They don’t act on the same objects

What are the four fundamental forces?

12.4 Universal Forces

12.1 Force12.4 Universal ForcesWhat are the four fundamental forces

Electromagnetic Forces Associated with charged particles Electric Force – between two charged

particles Negative and positive Opposites attract, like repels

Magnetic Force – between other magnets and certain metals

12.1 Force12.4 Universal ForcesWhat are the four fundamental forces

Strong Nuclear Force Act to hold the nucleus together Overcomes repulsion of positive protons

with each other The strongest force over small

(tiny, tiny) distances

12.1 Force12.4 Universal ForcesWhat are the four fundamental forces

Weak Nuclear Force Involved in certain types of radioactive

processes Active only over distances even smaller

than the strong nuclear force

12.1 Force12.4 Universal ForcesWhat are the four fundamental forces

Gravitational Force Between any two objects with mass Depends on the mass and the distance

between the objects Very weak force Acts over

very long distances