Friction Forces Inertia Gravity Chapter 10 - Forces

Friction Forces

Inertia

Gravity

Chapter 10 - Forces

Section 10.1 Motion and Forces

1) Force - Push or Pull; causes an object to move (Based on Strength and Direction)

a)Balanced Force - equal; no movementb)Unbalanced Force - causes a change in motion.c) Net Force - Combination of all forces.

Determines object's motion and direction. Acts in direction of greater force.Can show this with vectors.

2) Inertia - Tendency of object to resist change in motion.If Moving - will keep movingIf at rest - will stay at rest.

* The greater the mass, the greater the inertia; Greater force needed to change velocity

Physics of A Penny Lab

What is the Connection between MOTION and FORCE???

Explain why the penny and the paper behaved the way they did.

Using complete sentences,write a good scientific analysis in your notebook on left page

Friction - Any force that opposes motion.

4 Types of Friction:Static, Sliding,Rolling and Fluid.

Depends on type of surfaces and amount of force used.

Weightlessness occurs when a body is:1) falling freely in orbit;2) in outer space (far from a planet, star, or other massive body). There is no such thing as"Zero Gravity"

Gravity - Force exerted by one object on another.Dependent upon mass of objects and distance between them.

Gravity always pulls toward the center of the planet.Gravity on other planets is different from Earth because of the different masses.

*The bigger the mass, the stronger the gravitational pull, the more the object weighs.

Weight : Measurement of the gravitational force acting on an object.

Mass: Property of matter.

The difference between mass and force becomes obvious whenobjects are compared in different gravitational fields, such as away from the Earth's surface.

The SI unit of mass is the kilogram .The SI unit of force (weight) is the newton (N) (which can also be expressed in SI base units as kg·m/s² )

weight on different planets

1N = 1Kg x m/s/s

AIR RESISTANCE - (Fluid Friction) Air pressure exerted on object. (Upward Force)

Acts in OPPOSITE Direction of motion. Factors: Speed of object & Area of Object

TERMINAL VELOCITY: Point at which air resistance equals gravity. No further acceleration of object; motion continues. Highest velocity achieved by object.

(52 m/s before chute = 116 mph) (4.5 m/s after chute opens = 10 mph)

Free Fallin’ Objects: Tennis ball, marble, and index card

Drop each object (one at a time) from a height of 1 meter above the table.

Time how long the object takes

to “fall” to the floor. Start stopwatch- at release Stop-hits floor

Make predictions in your group about which object will have the longest/shortest falling times & why.

Tennis Ball

Marble Index Card

Time # 1

Time # 2

Create a table in your Notebook to record your results.

Be sure to answer these questions in your observations.

1) Why did index card take longer to hit the floor?

2) Were your times for the tennis ball and marble about the same time? Explain.

3) Write a statement describing how gravity acts or works on falling objects.

4) Bonus: Can you name of the Scientist who dropped cannon balls from the leaning tower of Pisa?

Early 1600’s: Legend says that Galileo dropped cannon balls of different weights, at the same time, from the top of the Leaning Tower of Pisa to find out which would hit the ground first.

What happened?? Did the heavier object hit the ground first? Or the lighter one?

The cannon balls hit the ground at the same time! We now know that all things fall at the same rate; gravity acts the same way on all objects regardless of their mass.

A projectile is: An object upon which the only force acting is

gravity.An object which once projected continues in

motion by its own inertia, and is influenced only by the downward force of gravity.

A projectile is: An object dropped from rest, orAn object which is thrown upwards at an angle

In the presence of gravity, the monkey also accelerates downward once he lets go of the limb.

Both banana and monkey experience the same acceleration since gravity causes all objects to accelerate at the same rate regardless of their mass.

Gravity Free Zone

With Gravity

In the absence of gravity, the banana moves in a straight line path (and does not experience any downward acceleration) and the monkey does not fall once he lets go of the tree.

Force is not required to keep an object in motion. Force is only required to maintain acceleration.

At what point does the projectile stop?

Circular Motion

Centripetal Force –

Force acting towards the center of a curved or circular path.

Why don’t I fall out when a roller coaster goes upside down?

Gravity is counteracted by the force of acceleration, which is the force that pushes you forward.

Balanced Forces!

Inertia: An object at rest will remain at rest, unless a force acts upon the object.

An object in motion will remain in motion, unless a force acts upon the object.

Tablecloth Trick:When you pull the cloth, friction acts on the objects in the direction of the pull.

Newton's First Law of Motion 1642 -1726

Start at 1:25

Newton's 3 laws of motion Explain common patterns of change in

motion. Analyze and predict changes in motion.

1:24

http://www.milkandcookies.com/link/138148/detail/

What happens to passengers when the car stops quickly?What happens to objects not safely secured??

Any object in motion will stay in motion until some force causes it to stop.

In this example, A seatbelt keeps the person in place when worn.Otherwise.....????

Newton's Second Law:Mass, Force and Acceleration. Net force acting on an object causes the object to

accelerate in the direction of the force.

Determined by: 1) Size of force ( More Force = More acceleration) 2) Mass of the Object ( More mass = More force

required)

Practice Problems:

What is the acceleration of a 3 kg object if a 18 N net force is applied?What is the acceleration of a 6 kg object if a 18 N net force is applied?

What conclusion can you draw about the relationship between Force, mass and acceleration?Answers:

F=m x a F=m x aF= 18N F = 18Nm= 3kg m= 6kga= F/m; 18N/ 3kg = 6m/s/s a= F/m; 18N/6kg = 3m/s/s

Newton's Third Law = For every action there is an equal and opposite

reaction.

Action- Reaction Pairs ( Act on different objects) Unbalanced Forces causes motion.

What are the pairs in these photos?

What is Momentum?

Momentum refers to moving things.

It is a product of the mass of an object and its velocity.

The greater the mass of the object, the more the momentum.

Momentum = Mass x Velocity P = m x V

kg . . m/s = kg x m/s

Law of Conservation of Momentum:Momentum before a collision is equal to the momentum after the collision.

Total Momentum: Sum of all objects moving together.CAN BE CALCULATED…

P1 + P2 + P3 = P total

StationaryMoving

A 15 kg object breaks apart into 3 equal pieces.1 part falls down at 3km/h, a 2nd part falls down at 5km/h, and the 3rd part falls down at 4km/h. What is the total momentum of all the pieces?

p=mxv

Piece #1

Piece #2

Piece #3

Getting Pushy LabLet's Get Rolling

How much time does it take to move

a given mass a given distance at a

given force???

Is constant force

needed to produce

constant speed?

SHOW ALL WORK......A car with a mass of 2500 kg traveling at a speed of 5 m/s collides with a truck with a mass of 7500 kg travelling at a speed of 20 m/s.

1. What is the car's momentum before the collision?2. What is the truck's momentum before the collision?3. What is the momentum of the system after the collision?

A car with a mass of 1500 kg and a speed of 10m/s collides with a 1200kg parked motorcycle.

1. What is the momentum of the car?2. What is the momentum of the motorcycle?3. What is the momentum of the system after the collision?