Bell Ringer Describe one station from yesterdays lab

Bell Ringer Describe one station from yesterday’s lab in detail.

Bell Ringer What is the difference between weight and mass?

NEWTON’S FIRST LAW

GALILEO ON MOTION • Laid the groundwork for Isaac Newton to develop his motion laws – Force: Any push or pull – Friction: Force acting between materials that touch as they move past each other • Always opposes direction of motion

GALILEO ON MOTION • Concluded that the tendency of a moving object to keep moving is natural – Inertia: The property that every object has to resist changes to its state of motion

GALILEO ON MOTION

Bell Ringer Give an example where inertia plays a role on the motion of an object.

ST NEWTON’S 1 LAW An object in motion will stay in motion, and an object at rest will stay at rest unless acted upon by a net, external force • Objects tend to keep doing what they’re already doing • Also called the Law of Inertia

MASS • Mass: A measure of the amount of inertia an object possesses – The • amount of matter in an object Units of Mass – Metric System: grams (g), kilograms (kg) – English System: slugs

MASS IS NOT VOLUME Volume: The amount of space an object takes up • Units of Volume – Metric System: liter (L), milliliter (m. L) – English System: quart, gallon… •

MASS IS NOT WEIGHT Weight Equation: weight = mass x gravity • So on Earth, 1 kg weighs 9. 8 N

NET FORCE The combination of all forces acting on an object • In the absence of a NET force: – Objects at rest, stay at rest – Objects in motion, stay in motion • Vector addition is used to find the net force acting on an object •

NET FORCE

Bell Ringer Which has more inertia 0. 5 g fly or a 50, 000 g bowling ball? How much does the bowling ball weigh? How much does the fly weigh?

EQUILIBRIUM When the net forces on an object sum to zero • Objects in equilibrium are either: – At rest – In motion at constant velocity • Objects require a net force in order to accelerate •

FREE BODY DIAGRAMS FBDs isolate the object of interest and analyze only the forces acting on the object • They are necessary to analyze the motion of an object due to the forces acting on it •

FREE BODY DIAGRAMS

FREE BODY DIAGRAMS Pushing Force (FP) Frictional Force (Ff) Normal Force (FN) Weight Force (FW)

Newton’s Second Law

Newton’s Second Law Force causes acceleration Force and acceleration are proportional As one increases, the other increases by the same amount

Newton’s Second Law Mass resists acceleration Objects with more inertia are less likely to change their states of motion Acceleration is inversely proportional to mass As mass increases, acceleration decreases by the same amount

Newton’s Second Law Force is equal to mass times acceleration SF = ma Where: SF = net force in Newtons m = mass in kilograms a = acceleration in m/s 2

Newton’s Second Law Note: The acceleration is always in the same direction as net force

Bell Ringer • What is the mass of a student who weighs 680 N? • What is their mass on 2 the moon? (1. 62 m/s )

Bell Ringer • Draw the FBD of a car stepping on the gas while going up a hill

Bell Ringer • A bug smashes into a truck’s windshield as it is driving at 80 mph. SWAAP!! • Which object experiences a larger force?

Newton’s Second Law Force is equal to mass times acceleration SF = ma Where: SF = net force in Newtons m = mass in kilograms a = acceleration in m/s 2

Thought Question • An old frail man approaches a worn bridge with his horse and wagon. He is worried that the tattered bridge will not hold up his wagon full of many rare and exotic birds. He ponders for a moment about what he can do in his dilemma and comes up with a solution. He swiftly shakes the bird cage and safely crosses the bridge. – What did this do?

Pressure: The amount of force per unit area • No matter what position you place a block on a table, it still applies the same force (weight) on that table

Pressure • To reduce pressure, you want to exert a large force over a large area • Pressure is calculated using the equation: Pressure = Force / Area OR P = F/A • Units: N/m 2 or Pascals (Pa)

Why do camels have such big feet? Larger surface area to distribute the force so they don’t sink into the sand

Bell Ringer 10/6 st • What is Newton’s 1 Law? nd • What is Newton’s 2 Law?

Friction Not restricted to solids, occurs in gases and fluids as well To move an object at constant velocity With Friction: An outside force must balance out the frictional force, making the net force zero Without Friction: An outside, net force is NOT needed (still making the net force zero)

Freefall Explained Solving F = ma for a, we get: F a= m The force of gravity and mass of an object are proportional and = to g F m and F m

Freefall and Air Resistance

Freefall and Air Resistance Air resistance is a force that counteracts the weight force for objects in freefall Consider a hammer and a feather: Unlike the hammer, the feather has a small weight, so air resistance quickly builds to equal its weight

Freefall Explained When air resistance equals the weight force, the net force acting is zero, and the object stops accelerating This is known as terminal velocity

Freefall and Air Resistance For a constant shape: Heavy objects take longer to reach terminal velocity than lighter objects For a constant weight: Smaller surface areas take longer to reach terminal velocity than larger surface areas

Freefall and Air Resistance

Freefall and Air Resistance

Bell Ringer • Why do heavier bodies “appear” to be falling faster than lighter ones?

Review Question • How much does a 60 kg person weigh? • How much force is required to lift this person?

Newton’s Third Law

Forces and Interactions • Forces do not act alone • They are interactions: Mutual actions between two objects • 2 forces will always act as partners (in pairs)

Forces and Interactions • Unlike mass, objects do not naturally possess force • Newton’s rd 3 Law states: Every action has an equal and opposite reaction

Identifying Action. Reaction Pairs • The “formula”: • ACTION: Object A exerts a force on object B • REACTION: Object B exerts a force on object A

Different Masses • Forces acting on different objects are ALWAYS equal and opposite • It is mass that causes objects to behave differently • According to Newton’s 2 nd Law, varying the mass to which the force is applied will vary its acceleration

Different Masses Consider the following: • A cannon has mass = m • A cannonball has mass = m • When fired, the cannon applies a force to the cannonball that is equal and opposite to the force the cannonball applies back on the cannon

Different Masses So why does the cannonball have a large acceleration while the cannon recoils only slightly? CANNONBALL: CANNON: F/m = a Given the same force, smaller masses will accelerate at a greater rate

Bell Ringer What is the action/reaction pair for a skydiver jumping out of a plane?

Rocket Final Build Day Review your rubric Test your recovery system Fit your rocket for the launcher Make sure all parts are secure Make sure your pressurized bottle does not have any defects. `Plagarism

Bell Ringer What is your total net force? How did Newton’s 3 rd law affect your rocket? What happens to your car as a bug smashes into your windshield?

Gravitational Force Attractive force between all pieces of matter Newton’s Law of Gravitation Every particle in the universe exerts an attractive force on every other particle equal to: F=G m 1 m 2 r 2

Newton’s Law of Universal Gravitation F=G m 1 m 2 r 2 -11 2 2 Where G = 6. 673 x 10 N·m /kg Universal gravitational constant m 1 and m 2 are the masses of each particle r is the distance between the particles

Thought question. The Physic’s diet… “You can easily loose weight within the matter of seconds with my weight loss program. ” How is this possible?

Newton’s Law of Universal Gravitation

Other Useful Constants Mass of the Earth (m. E): 24 5. 98 x 10 kg Radius of the Earth (r. E): 6 6. 38 x 10 m Mass of the Moon (m. M): 22 7. 35 x 10 kg

Sample Problem What is the gravitational force between the Earth and the Moon? At its closest point, the Moon is only 363, 104 km (225, 622 miles). And at its most distant point, the Moon gets to a distance of 406, 696 km (252, 088 miles).

Weight and Mass Weight: The gravitational force that is exerted on an object Always acts directly downward Fg = G m. E · m Fg = m · g r. E 2 For objects “close” to the surface

Sample Problem What is the gravitational force between the Earth and the Moon?

Bell Ringer “Superman's ability to fly has been explained as a result of Earth's gravity being much less than that of his home world…” Krypton, Superman’s planet of origin and about the same size as earth, is said to have a gravitational pull 15 times larger than Earth. If Superman’s mass is 90. 0 kg, what is the mass of Krypton?

Gravitational Force Attractive force between all pieces of matter Newton’s Law of Gravitation Every particle in the universe exerts an attractive force on every other particle equal to: F=G m 1 m 2 r 2

Newton’s Law of Universal Gravitation F=G m 1 m 2 r 2 -11 2 2 Where G = 6. 673 x 10 N·m /kg Universal gravitational constant m 1 and m 2 are the masses of each particle r is the distance between the particles

Thought question. The Physic’s diet… “You can easily loose weight within the matter of seconds with my weight loss program. ” How is this possible?

Bell Ringer A 60 kg boy and 40 kg girl are sitting 2 m apart. Assuming that the force of attraction is caused by the universal gravitational force, how great is the force between them?