Forces What are forces Inertia Gravity Newtons Laws

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Forces What are forces? Inertia Gravity Newton’s Laws Projectile motion

Forces What are forces? Inertia Gravity Newton’s Laws Projectile motion

What is a force? n. A push or a pull n May be unbalanced

What is a force? n. A push or a pull n May be unbalanced or balanced

What does a force do? n Gives energy to an object n Can set

What does a force do? n Gives energy to an object n Can set an object in motion, make it stop, or change its motion

Unbalanced forces change motion

Unbalanced forces change motion

Unbalanced forces change motion

Unbalanced forces change motion

Unbalanced forces change motion

Unbalanced forces change motion

Forces are represented by vectors

Forces are represented by vectors

Forces are added with vectors

Forces are added with vectors

Friction n. A force which opposes motion, bringing objects to rest n Types:

Friction n. A force which opposes motion, bringing objects to rest n Types:

Inertia

Inertia

Inertia n The tendency of an object to stay at rest or in motion.

Inertia n The tendency of an object to stay at rest or in motion. n Objects with greater mass have greater inertia

Inertia keeps astronauts in motion

Inertia keeps astronauts in motion

Seat belts protect against inertia

Seat belts protect against inertia

Gravity

Gravity

Gravity The attractive force between all objects in the universe

Gravity The attractive force between all objects in the universe

F = M 1 M 2 d 2 n More mass means greater gravity

F = M 1 M 2 d 2 n More mass means greater gravity n More distance means less gravity Massive objects have lots of gravity My gravitational attraction is small no matter what the distance!

The earth exerts a force on the student and the student exerts a force

The earth exerts a force on the student and the student exerts a force on the earth because of GRAVITY!

Newton’s Laws of Motion 1. Inertia 2. F=ma 3. Action-reaction

Newton’s Laws of Motion 1. Inertia 2. F=ma 3. Action-reaction

Newton’s First Law of Motion n The law of inertia: An object at rest

Newton’s First Law of Motion n The law of inertia: An object at rest stays at rest an object in motion stays in motion unless acted upon by an outside force.

Inertia keeps astronauts in motion

Inertia keeps astronauts in motion

Inertia keeps satellites in orbit

Inertia keeps satellites in orbit

Inertia keeps you at rest

Inertia keeps you at rest

Newton’s Second Law of Motion n Force = Mass x acceleration n A force

Newton’s Second Law of Motion n Force = Mass x acceleration n A force is needed for acceleration n Acceleration will occur in the direction of the force.

Which cars are accelerating? n If you watch carefully, the green and blue cars

Which cars are accelerating? n If you watch carefully, the green and blue cars are accelerating. The red car is traveling at constant speed.

A force is needed for acceleration Will these accelerate? n A skier going downhill?

A force is needed for acceleration Will these accelerate? n A skier going downhill? – What force is acting on the skier? n An astronaut on a spacewalk? – Are any forces acting on the astronaut? n

Which of the following will accelerate? n. A bullet shot from a gun? –

Which of the following will accelerate? n. A bullet shot from a gun? – What forces are acting on the bullet? A hammer and feather dropped on the moon? – What force is acting?

Newton’s 2 nd Law Force = mass x acceleration F_____ M A Force is

Newton’s 2 nd Law Force = mass x acceleration F_____ M A Force is measured in newtons. A newton is a kg m s 2 n n Example: A car with mass 1000 kg hits a tree and decelerates at 50 m/s/s. What force does it exert on the tree?

Answer: M F_____ A 1000 kg * 50 m/s/s = 50, 000 kgm or

Answer: M F_____ A 1000 kg * 50 m/s/s = 50, 000 kgm or 50, 000 N s 2

F = ma n. A car is traveling at constant speed. Is a force

F = ma n. A car is traveling at constant speed. Is a force acting on it? n Answer: although there are forces acting on the car (gravity, friction, air resistance, etc…) since there is no acceleration, the net force in the direction of motion must be zero.

More 2 nd Law Problems: n 1. What is the acceleration on a mass

More 2 nd Law Problems: n 1. What is the acceleration on a mass of 50 kg if a force of 10 N is applied? n 2. An object accelerates due to gravity at a rate of 10 m/s/s. If its mass is 15 kg, what force is acting on the mass?

Answers: n _F_ M A 1. _10 N_ 0. 2 n/kg= 0. 2 kg

Answers: n _F_ M A 1. _10 N_ 0. 2 n/kg= 0. 2 kg m = 0. 2 m/s 2 50 kg A s 2/kg 2. F______ 15 kg 10 m/s 2 150 kgm/s 2 or 150 N

Gravity is a force that causes an acceleration n On earth, ALL objects accelerate

Gravity is a force that causes an acceleration n On earth, ALL objects accelerate at 9. 8 m/s 2 (ignoring air resistance) because of gravity. n No matter what the mass, ALL objects on earth accelerate at 9. 8 m/s 2

Newton’s 2 nd Law n 3. F__ m a An object of mass 3

Newton’s 2 nd Law n 3. F__ m a An object of mass 3 kg falls off a cliff. How much force is acting on the object? Answer: F_______ 3 kg 9. 8 m/s 2 29. 4 N

Free fall without air resistance Both the elephant and the feather land at the

Free fall without air resistance Both the elephant and the feather land at the same time!

Free fall with air resistance The feather takes lots longer to hit the ground!

Free fall with air resistance The feather takes lots longer to hit the ground!

Newton’s Third Law n For every action, there is an equal and opposite reaction

Newton’s Third Law n For every action, there is an equal and opposite reaction

For every action, there is an equal and opposite reaction n In rocketry…… The

For every action, there is an equal and opposite reaction n In rocketry…… The gases being expelled is the action. The rocket propelling forward is the reaction.

How do Newton’s laws describe the motorcycle rider? n 1 st: Inertia keeps the

How do Newton’s laws describe the motorcycle rider? n 1 st: Inertia keeps the rider moving forward. n 2 nd: The force with which the rider hits the ground will be equal to his mass times his deceleration. n 3 rd: The action of hitting the ground will equal the reaction of the dirt.

Projectile motion

Projectile motion

Projectile motion n An object moves forward due to inertia and accelerates downward due

Projectile motion n An object moves forward due to inertia and accelerates downward due to gravity.

Projectile motion of a ball fired vertically The motion of the truck causes the

Projectile motion of a ball fired vertically The motion of the truck causes the ball to project forward. What would happen if the truck stopped?

In this video, the ball is dropped straight down and moves forward due to

In this video, the ball is dropped straight down and moves forward due to inertia

Package dropped from plane The forward motion of the plane causes the package to

Package dropped from plane The forward motion of the plane causes the package to land in front of where it’s dropped.

Satellites

Satellites