Forces - Study Guide for Quiz

1. What should I study for my quiz on FORCES?

2. Welcome to a WinteryWednesday • Come IN QUIELTY AND WRITE YOUR HOMEWORK DOWN!!!! • WHICH IS TO FINISH YOUR CHAP. 17 GRAPHIC ORGANIZER. • THEN COMPLETE PAGE 631 QUESTIONS 1 (A-C) AND 2 (A & C). REMEMBER TO WRITE THE QUESTION AND USE COMPLETE SENTENCES!!!

3. Terrific Thursday • Come IN QUIELTY AND WRITE YOUR HOMEWORK DOWN!!!! Which is to complete friction foldable. • Heads up!!! Chapter 17 Spelling Test will be on 12/18/07 • Take out your graphic organizer from yesterday. • Get ready to rock-n-roll.

4. Welcome to a Freezing Friday • Come in QUIETLY!!!!!!!! Do the following: • Write down your homework which is none. • Take out your Chap 17. section 1 and 2 graphic organizer. • Reminders your Chapter 17 spelling test will be on 12/18. • Also if you have not made up your Chapter 16 Test please do so by 12/11/07. Those people are: C. Mayo, T. Street, M. Larcosse, and C. Cotes. CJ Flowers, I.Allen, and N. Disla SEE ME ASAP!!!

5. FORCES When you ride a bike, your foot PUSHES against the pedal. The push makes the wheels of the bike move. When you drop something, it is PULLED to the ground by gravity. A FORCE is a PUSH or PULL in a particular DIRECTION.

6. BIG SCIENCE IDEA FORCES FORCES AFFECT HOW OBJECTS MOVE. • Forces can affect motion in the following ways: They can make objects: • START MOVING • MOVE FASTER • MOVE SLOWER • STOP MOVING • CHANGE DIRECTION • CHANGE SHAPE

7. FORCES Since forces cause changes in SPEED or DIRECTION of an object, we can say that forces change MOTION, so…. Forces cause ACCELERATION.

8. FORCES More than one force can act on an object at one time. What happens to the object when forces act depends on 2 things: 1) Strength of the Forces 2) Direction of the Forces

9. If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED. FORCES If the forces don’t cancel each other out – 1 force is stronger than the others – the forces are UNBALANCED and will cause a CHANGE IN MOTION.

10. + = 5 N right 5 N right 10 N right COMBINING FORCES Two forces in the same direction can add together to produce a larger NET FORCE.

11. - = 5 N right 10 N left 5 N left COMBINING FORCES Two forces in opposite directions can subtract to produce a smaller net force in the direction of the larger force.

12. 5 N right 5 N left COMBINING FORCES Two forces may cancel each other out (if equal and opposite) to produce NO NET FORCE. 0 N (No Net Force) + =

13. Review - What is Friction? • Friction is a force that two surfaces exert on each other when they rub against each other. • The direction of the friction force is always OPPOSITE to the direction of the motion. • It SLOWS down moving objects! Direction of Motion Friction Force

14. Types of Friction • Static Friction opposes the motion of an object that is at rest • To make the object move, you have to exert a force larger than the force of static friction. Direction of Intended Movement Static Friction Force

15. Types of Friction • Sliding friction occurs when two solids slide over each other. • Sliding friction makes car brakes work and stops athletes from slipping. Sliding Friction Force Direction of Slide

16. Types of Friction • Rolling friction occurs when an object rolls across a surface. • Rolling friction is easier to overcome than sliding friction for the same materials. Direction of Motion Friction Force

17. Types of Friction • Fluid friction occurs when a solid object moves through a liquid or gas. • Air resistance is a type of fluid friction. Direction of Motion Friction Force

18. Review - What is Friction? • Friction is a force that two surfaces exert on each other when they rub against each other. • The direction of the friction force is always OPPOSITE to the direction of the motion. • It SLOWS down moving objects! Direction of Motion Friction Force

19. The Force of Gravity • Gravity is the force that pulls all objects down to the earth. • Rain falls from the sky down to earth… • If you drop a book, it falls to the ground… • If you trip, you’ll fall down…

20. Universal Gravitation • Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book) • The force of gravity is much STRONGER for LARGER objects (more mass).

21. Universal Gravitation • Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction... • So, no matter where you are on earth, all things fall to the ground due to gravity…

22. What is “free fall”? • When gravity is the ONLY force acting on an object, it is in free fall. • In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate.

23. Acceleration due to Gravity • Calculate the acceleration of an object in free fall. A = Final speed – initial speed time A = 50 m/s – 0 m/s 5 s Acceleration = 10 m/s2

24. What is “free fall”? • ALL objects in free fall travel at the same rate regardless of their mass… • Heavy objects fall at the same rate as light objects! • Let’s try it!

25. WHY does the penny land first? • Remember the force that opposes motion (slows things down)? FRICTION! • Falling objects experience friction with the air called AIR RESISTANCE that slows them down. So, which will land first?

26. Air Resistance • The larger the object (more surface area), the more air resistance. • That’s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall.

27. Air Resistance Gravity • Draw a diagram showing the forces… • Downward force of gravity is same on both. • Upward force of air resistance is greater on the feather. • The net force (down) is greater on the penny. Air Resistance Net Force on Penny Net Force on Feather

28. Without air resistance, all objects would fall at the same rate… Galileo Drops the Ball Hammer and Feather Drop on the Moon

29. Air Resistance = 800 N Draw a free body diagram of the sky diver and label ALL the forces. Gravity = 1000 N Air Resistance = 800 N What is the net force? Net Force = 200 N Gravity = 1000 N