GRAVITY NOT AS OBVIOUS AS IT SEEMS Misconceptions

GRAVITY IS A WEAK FORCE • Electromagnetic force > force of earth’s gravity • Really? Really! Otherwise, we’d be a puddle • the EM force keeps atoms together, despite gravity wanting to tug them all to the earth • More on this in a bit http: //www. youtube. com/watch? v=BQA 5 VDXE 7 ts

TWO SCHOOLS OF THOUGHT Aristotle: reasoning-based Galileo: empirical evidence • Objects fall at different rates due to their different masses • Objects fall at the same rate so long as air resistance is equal • Neglected to consider other variables that affect the rate of fall • Air resistance establishes terminal velocity – max rate of fall http: //www. youtube. com/watch? v=AYz_K 3 mwq 6 A

WHY NOT MASS? • Apply Newton’s laws of Motion: • #2: Force = mass x acceleration aka a = F/m • Where: • mass is the falling object • the force is gravity between object and Earth • the fall is the acceleration • #1: More mass has greater inertia, requires more force to move it • a proportional relationship between force and mass • therefore objects fall at same rate 2 m/s (rate of fall) = 2 N 1 Kg smaller mass = 20 N 10 Kg bigger mass

NEWTON, ROUND 2 • Gravity is not restricted to objects falling to earth • Every object in the universe exerts a gravitational force on everything else • aka Universal Gravitation Isaac Newton Minute. Physics

THE G-FORCE IS VARIABLE • Gravitational force depends on: - masses of the objects - the distance between them • Mass is proportional to force of gravity; greater masses have a greater g-force between them • Distance is inversely proportional to force of gravity; at greater distances, force between masses is lower

THEREFORE: FORCE CHANGES AS OBJECTS FALL TO EARTH • Distance is reduced as an object falls • Force increases proportionately • Causes constantly increasing acceleration of fall • Use: a=F/m • a = 10 N/2 kg greater distance apart vs a= 100 N/2 kg less distance apart

HOW FAST? Terminal velocity • Max rate with air resistance • When resistance = g-force of fall; no addl. acceleration • Increase resistance causes a slow down http: //www. youtube. com/watch? v=5 c. PFXag. NCe 4 Free fall • Without air resistance • No variables affect rate http: //www. youtube. com/watch? v=KDp 1 ti. Us. Zw 8

FREE FALL t 1 t 2 t 3 t 4 t 5 http: //www. youtube. com/watch? v=x. Q 4 zn. Shl. K 5 A • With no resistance object falls faster and faster • Acceleration of 9. 8 m/sec • increasing distance each second http: //www. youtube. com/watch? v=Otxl. QTmx 1 LE

SO WHAT? • The relationship has two dependent variables: • How much area is the force (gravity, spray paint…) spread out over? • What is the power/intensity of the force (light, radiation…) per area unit? • At increasing distance, the effect of the force (paint, sound, gravity…) is spread, much more thinly, over a much larger area

INVERSE SQUARE LAW • The relationship between these variables is the inverse square law • Governs G force as well as: : • Sound http: //auditoryneuroscience. com/acoustics/inverse_square_law • Light http: //www. youtube. com/watch? v=f. F 74 gh. L 8 txw • http: //bcs. whfreeman. com/universe 7 e/content/ch 19/1903002. html • Radiation http: //zebu. uoregon. edu/images/cowbomb. mpg • Paint http: //www. mrwaynesclass. com/teacher/Gravity/Inverse. Square/ • Butter? http: //www. youtube. com/watch? v=JW 3 t. T 0 L 2 gpc

As the paper is moved away from the candle; what happens to the number of squares illuminated? What happens to the brightness on each square? How many squares will be lit up at 4 feet? Bonus; What is the percentage of light on any one square at 4 feet?