air resistance is a form of friction that acts to slow down any object moving in the air. air...

• Air resistance is a form of friction that acts to slow down any object moving in the air.

• Air resistance is a force that gets larger as an object moves faster.

• Air resistance also depends on the shape of an object.

Air Resistance: a.k.a. Fluid Friction

• When an object falls, it speeds up as gravity pulls it downward.

• At the same time, the force of air resistance pushing up on the object is increasing as the object moves faster. • Finally, the upward air resistance force becomes large enough to equal the downward force of gravity!

Fluid Friction, continued

• When the air resistance force up equals the gravitational force down (weight), the net force on the object is zero. • So According to Newton’s laws of motion, the object’s acceleration would be zero, and its speed no longer increases.

Fluid Friction, continued

Terminal Velocity• Terminal Velocity is

the maximum speed an object travels when falling (e.g. “terminal” meaning: END)

• Terminal velocity is reached when the object no longer accelerates, but is traveling at a constant speed because the force of air resistance pushing up balances the force of gravity pulling down.

• Sometimes forces and motion are not in a straight line.

Projectile Motion

• When throwing an object, the horizontal force from the throw propels the object forward while the gravitational force pulls the object downward. • The net force thus acts at an angle to the direction the object is moving, and so the object follows a curved path.

Projectile Motion, continued

• Projectile motion is the curved path an object follows when thrown or propelled forward. It has BOTH a horizontal force AND vertical force component.

• Examples: shooting a basketball, a leaping frog, a catapult, aiming at a target.

• The faster an object is thrown, the farther it travels before gravity pulls it to Earth.

• CIRCULAR MOTION is the motion of an object in a circle.

• If you are in circular motion, your direction of motion is constantly changing, thus the object is accelerating.

Circular Motion

• If an object is constantly accelerating, there must be a force acting on the object the entire time.

Circular Motion, continued

• Opposing inertia is a force called centripetal force which pulls an object inward toward the center of the circle.

• In circular motion the centripetal force is always perpendicular to the forward motion.

• Due to inertia, your body wants to propel forward in a straight line as the merry-go-round turns.

• Gravity is an attractive force that pulls objects toward each other.

• Gravity depends on the mass of the objects and the distance between them.• The gravitational force stronger: larger objects; closer objects

Gravitational Force

• The gravitational force weaker: smaller objects; farther away objects

• Only Earth is close enough and massive enough to exert a noticeable gravitational force on you.

• The force of gravity between you and Earth is about 1,650 times greater than between you and the Sun.

Gravitational Force, continued

• The force of gravity causes all objects near Earth’s surface to fall with an acceleration of 9.8 m/s².

Satellite Motion • Satellites go

around Earth in nearly circular orbits, with the centripetal force being gravity.

• A satellite’s motion is like that of a baseball, gravity pulls inward toward the earth and inertia causes the object to continue moving forward.

Satellite Motion

• The speed at which an object must move to go into orbit near Earth’s surface is about 8 km/s, or about 29,000 km/h. HAVE YOU EVER SEEN A SATELLITE IN THE NIGHT SKY?

________________ pulls an object inward toward the center of a circle.

A. Projectile MotionB. Satellite MotionC. Circular MotionD. Centripetal Force

Question 1

Answer

The answer is D, “centripetal force.”

Question 1

________________ pulls an object inward toward the center of a circle.

Describe how an object has curved motion.

Question 2

Answer

Once an object is moving forward, inertia causes the object to continue forward. Centripetal force pulls the object inward. The two forces create a curved net force.

Describe how an object has curved motion.

Question 2

Momentum• When two or more

objects interact, momentum may be exchanged, but the total amount of momentum does not change.

• Momentum is a measure of how difficult it is to stop a moving object. In other words, momentum in the strength of an objects motion.

• It equals the product of mass and velocity (p = mv)

Calculations of Momentump = mv

• In this equation, p = momentum (kg ∙ m/s); m = mass (kg); and v = velocity (m/s)

• Calculate the momentum of a 14 kg bike traveling north at 2 m/s.

p = mv28 kg ∙ m/s northp = (14 kg)(2 m/s) =

p = ? m = 14kg v = 2m/s north


•A 10,000 kg train in traveling east at 15m/s. Calculate the momentum of the train.

p = mv

150,000 kg ∙ m/s east

p = (10,000 kg)(15 m/s) =

p = ? m = 10,000kg v = 15 m/s east


•What is the momentum of a car with a mass of 900 kg traveling south at 27 m/s?

p = mv

24,300 kg ∙ m/s south

p = (900 kg)(27 m/s) =

p = ? m = 900kg v = 27 m/s south

In your own words, what is momentum?

Question 3

Answer

• Momentum is a measure of how difficult it is to stop a moving object. In other words, momentum in the strength of an objects motion.

Question 3

In your own words, what is momentum?

What is the formula for momentum?

Question 4

Answer

p = mv (momentum = mass * velocity)

Question 4

What is the formula for momentum?