Friction

1. Gravity Inertia Chapter 10 - Forces Friction Forces

2. 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 movement b)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 moving If at rest - will stay at rest. * The greater the mass, the greater the inertia; Greater force needed to change velocity

3. 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

4. Friction - Any force that opposes motion. Depends on type of surfaces and amount of force used. 4 Types of Friction:Static, Sliding,Rolling and Fluid.

5. 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. 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"

6. Weight : Measurement of the gravitational force acting on an object. Mass: Property of matter. weight on different planets The difference between mass and force becomes obvious when objects 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 ) 1N = 1Kg x m/s/s

7. AIR RESISTANCE - (Fluid Friction) Air pressure exerted on object. (Upward Force) Acts in OPPOSITEDirection 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)

8. Free Fallin’ Objects • 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.

9. Free Fallin’ Data • 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?

10. Free Fall & Galileo Galilei • 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.

11. PROJECTILES A projectile is: An object upon which the only force acting is gravity. An object which once projectedcontinues in motion by its own inertia, and is influenced only by the downward force of gravity. A projectile is: An object dropped from rest, or An object which is thrown upwards at an angle

12. With Gravity 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 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.

13. Force is not required to keep an object in motion. Force is only required to maintain acceleration. At what point does the projectile stop?

14. Circular Motion Centripetal Force – Force acting towards the center of a curved or circular path.

15. 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!

16. Newton's 3 laws of motion Explain common patterns of change in motion. Analyze and predict changes in motion. Newton's First Law of Motion 1642 -1726 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. 1:24 Start at 1:25 http://www.milkandcookies.com/link/138148/detail/

17. 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.....????

18. 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)

20. 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 a F= 18N F = 18N m= 3kg m= 6kg a= F/m; 18N/ 3kg = 6m/s/s a= F/m; 18N/6kg = 3m/s/s

21. 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?

22. 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

23. 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

24. Moving Stationary

25. 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

26. Getting Pushy Lab Let's Get Rolling Is constant force needed to produce constant speed? How much time does it take to move a given mass a given distance at a given force???

29. 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?