1. Conceptual Physics http://mrlafazia.com/PHYS111/lessons/201011Fall/PHYS111_12.ppt THURSDAY September 30 th, 2010 LESSON GOALS: Discuss nature of Forces Look at history of Galileo and his contributions to Force concepts Run Interactive Physics simulation 6.3 Complete real-life experience discussion prompt Review important definitions (with corresponding simulations) Read Poem Newton Stole the Limelight Take a quick quiz 1/19

2. Discussion “What is a force”? – Is it a physical thing? – Are there many types? – Is there a single equation that describes forces? “How do forces relate to our Energy concepts”? 2/19

3. Galileo Galilei on Inertia a MrLaFazia.com original snapshot SOURCE: http://www.cartoonstock.com/newscartoons/cartoonists/bro/lowres/bron1636l.jpg NOTE: Galileo lived from 1564 to 1642… NOT 1489! 3/19

4. Introduction & Overview Galileo’s life teaches us many things – (not the least of which is—DON’T STARE AT THE SUN THROUGH A TELESCOPE!) For today, however, we will discuss his ideas on MOTION 1) the Leaning Tower of Pisa 2) defining Force and the role of friction 3) Inertia (ramp experiments) 4/19

5. The Leaning Tower of Pisa This tower portion is considered “legend,” of course…but... Wherever he dropped the objects, Galileo showed that less massive objects fall at the same rate as more massive ones – air resistance must either be equal or eliminated SOURCE: http://improbable.com/airchives/paperair/volume15/v15i3/v15i3-web- images/KIM-Galileo_of_the_lem_opt.jpeg 5/19

6. Defining “Force” Forces are most simply defined as – A PUSH – Or A PULL It was once believed that forces were needed to KEEP objects in motion. – People believed this because life taught them that objects slow down and eventually stop (like your car not moving) unless a force keeps them going. Galileo showed that objects need no force to maintain their motion. – What people originally had not realized was the fact that friction is a FORCE as well! The fact is: Forces that aren’t balanced out will ALWAYS cause a change in any object’s motion (whether speeding up or slowing down or changing direction)! SOURCE: http://goozydumps.files.wordpress.c om/2008/09/galile os_experiment.jpg 6/19

7. Inertia Galileo did a number of experiments to test his theories of forces and motion: 7/19

8. SOURCE: http://www.cartoonstock.com/cartoonview.a sp?catref=mhen235 8/19

9. Inertia Imagine if a ball were allowed to roll down a ramp and roll right onto a level ramp. – Without a force to slow it down or speed it up, what would happen to its motion? THIS is the concept of “inertia.” – What would be needed to speed up the ball? – What would be needed to slow down the ball? – ______________ slow down the ball in the real world. This does NOT violate the concept of Inertia, but rather justifies it! Frictional Forces 9/19

10. The Law of Inertia 10/19

11. Forces…Motion…& Energy? Do the results of the ramp experiments (see page 32, Figure 3.4 of Conceptual Physics, if applicable) match up with our understanding of the Conservation of Energy (“Total Energy is Boring”) Principle? Perhaps you have heard the formation of these concepts attributed to Sir Isaac Newton or another scientist, before. There is a someday- famous poem which describes this misconception quite well. I will read it to you at the end of the class. STAY TUNED! 11/19

12. A Final Bit of Humor SOURCE: http://emdashes.com/assets_c/2 010/04/Galileoroll2-thumb- 182x224.png 12/19

13. Interactive Physics Open and view Simulation 6.3…. 13/19

14. Discuss With A Partner “Describe an experience you have had in life where you have had the following things happen (or have caused these things to happen)” : Had to keep an object moving (how did you do this?) Had to keep an object FROM moving (how did you do this?) Had to stop an object while it was already IN motion (again, how did you do this?) Try to provide a name (of your own choosing) for each force involved! 14/19

15. Definitions (w/ Simulations) – Mass vs. Weight PLEASE learn the difference. – European scales? – American vs. European Scales on the Moon? Simulation: Interactive Physics 4.1; 4.2. – Inertia Note that this is NOT an actual “quantity.” Simulation: Interactive Physics 6.4. – Net-Force Simulation: Interactive Physics 6.5; 6.6. – the Equilibrium Rule possible both while moving AND while not moving – terminal speed (or “terminal velocity”) Simulation: Interactive Physics 5.1; 5.2. – support force also known as the “normal” or “perpendicular” force – I primarily call it the “Normal” force…just so you know. 15/19

16. Poem: Newton Stole the Limelight, by D. LaFazia 16/19 The English stole the limelight While history is clear That an Italian earned the copyright To the Physics law presented here. A generation before Newton --knighted though he was-- Galileo Galilei Had already killed Newton's buzz. Take Newton's Law of Inertia (you can steal it like he did). This "1st Law" as they call it Was discovered before Newton was a kid. Galileo knew that objects Simply do not change their speed Unless something else acts on them To precipitate this need. So objects that are moving Will keep moving as they were And objects standing still at first Need a force to make them stir. You may not know of Newton's 2nd Or even of his 3rd, But when you hear of his blatant copying You'll mark him as a lying, stealing nerd. Now my aim is not to disrespect Or slander Newton's name. His contributions rightly earn him A considerable amount of fame. All that I am saying (and on this I must be right) Is that the English are plainly guilty Of stealing Italy's limelight. Forza Italia !

17. Quick Quiz “A parachutist jumps out of an airplane from the usual height (under 3 miles above the Earth’s surface). She is of average size and mass. Describe her descent in the real world (with air resistance) at the following segments of her fall”: What happens during the time from when she has just jumped out of the plane to just before she pulls the ripcord to deploy her ‘chute? In the first few moments during and after she pulls the ripcord to deploy her ‘chute, does she (choose the appropriate response) – Fall faster – Rise upward suddenly – Fall slower – Experience no change in her motion? Would her eventually-reached terminal velocity be more, less, or remain unchanged if she had never opened the ‘chute? BONUS) Describe how the parachute would respond and affect her descent if there were no air resistance. 17/19

18. Recommended Reading: Sections 3.2-3.7 Sections 4.1-4.4 These sections of the text prepare you for the Force concepts from Unit 2. We will look more at the motion concepts in later lessons within Unit 2. 18/19

19. Looking Ahead: 19/19 Next class we will take a closer look at Force concepts by exploring Newton’s Laws of Motion. You will also be assigned HMWK #5 next class.