DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

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1 DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

2 TSOKOS LESSON 6- THE LAW OF GRAVITATION

3 Essential Idea: The Newtonian idea of gavitational foce acting between two spheical bodies and the laws of mechanics ceate a model that can be used to calculate the motion of planets.

4 Natue Of Science: Laws: Newton s law of gavitation and the laws of mechanics ae the foundation fo deteministic classical physics. These can be used to make pedictions but do not explain why the obseved phenomena exist.

5 Theoy Of Knowledge: The laws of mechanics along with the law of gavitation ceate the deteministic natue of classical physics. Ae classical physics and moden physics compatible? Do othe aeas of knowledge also have a simila division between classical and moden in thei histoical development?

6 Undestandings: Newton s law of gavitation Gavitational field stength

7 Applications And Skills: Descibing the elationship between gavitational foce and centipetal foce Applying Newton s law of gavitation to the motion of an object in cicula obit aound a point mass

8 Applications And Skills: Solving poblems involving gavitational foce, gavitational field stength, obital speed and obital peiod Detemining the esultant gavitational field stength due to two bodies

9 Guidance: Newton s law of gavitation should be extended to spheical masses of unifom density by assuming that thei mass is concentated at thei cente Gavitational field stength at a point is the foce pe unit mass expeienced by a small point mass at that point Calculations of the esultant gavitational field stength due to two bodies will be esticted to points along the staight line joining the bodies

10 Data Booklet Refeence: Mm F G F g m M g G

11 Utilization: The law of gavitation is essential in descibing the motion of satellites, planets, moons and entie galaxies Compaison to Coulomb s law (see Physics sub-topic 5.1)

12 Aim 4: The theoy of gavitation when combined and synthesized with the est of the laws of mechanics allows detailed pedictions about the futue position and motion of planets

13 Intoductoy Video The Foce of Gavity

14 Newton s nd Law Newton s second law (F=ma) implies that if a mass is acceleating, thee must be a foce acting on it An object falls (acceleates towad the eath) because of gavity What holds planets in thei obits?

15 Newton s nd Law Newton s second law (F=ma) implies that if a mass is acceleating, thee must be a foce acting on it An object falls (acceleates towad the eath) because of gavity What holds planets in thei obits? Gavitational Foce

16 Newton s Law of Gavitation The attactive foce between two point masses is, Whee, F G M M M1 and M ae the masses of the attacting bodies is the distance between them 1 G is Newton s constant of univesal gavitation and has a value of x N m kg -

17 Newton s Law of Gavitation The diection of the foce is along the line joining the two masses,

18 Newton s Law of Gavitation The fomula applies to point masses, which means the masses ae small in elation to the sepaation between them

19 Newton s Law of Gavitation When the adii of two planets is small in compaison to the distance between them, we conside them to be point masses

20 Newton s Law of Gavitation What is the gavitational foce between the eath and the sun?

21 Newton s Law of Gavitation What is the gavitational foce between the eath and the sun? F F ES M1M G 3.5x10 N M M E S 5.98x x10 1.5x10 11 m 4 30 kg kg

22 Newton s Law of Gavitation How does this compae to the gavitational foce between the eath and you? F F ES M1M G 3.5x10 N

23 Newton s Law of Gavitation How does this compae to the gavitational foce between the eath and you? F F F ES EYou M1M G 3.5x x10 N N M M E E You 5.98x10 75kg 3.38x m kg

24 Newton s Law of Gavitation Since F=ma, what value of a does this yield? F F F ES EYou M1M G 3.5x x10 N N

25 Newton s Law of Gavitation Since F=ma, what value of a does this yield? F F F ES EYou M1M G 3.5x x10 Sound Familia? N N F a m a you ma F m kg

26 Gavitational Field Stength The gavitational field stength at a cetain point is the foce pe unit mass expeienced by a small point mass, m, at that point. M1m F G F ma M1m ma G M1 a G

27 Gavitational Field Stength The units of gavitational field stength ae Nkg -1 1N = 1 kg m s - So units become m s -, acceleation! M1m F G F ma ma G a g M1m M G 1

28 Gavitational Field Stength Gavitational field stength is a vecto quantity whose diection is given by the diection of the foce a point mass would expeience if placed at the point of inteest.

29 Gavitational Field Stength The gavitational field stength aound a single point mass is adial which means it is the same fo all points equidistant fom the cente of mass and diected towad the cente.

30 Gavitational Field Stength On a mico- vesus macolevel (like the pojectile motion of a football), the field stength can be consideed to be unifom with a constant value.

31 The Law of Gavitation and Planetay Motion

32 Obital Motion In ode fo a body to move in a cicula o elliptical path, thee must be a foce to cause centipetal acceleation Fo planets, that foce is the foce of gavity F F m G v Mm G ma m Mm v

33 Obital Motion Solving fo v, we get the velocity a body must maintain to emain in an obit m v v G GM Mm v GM

34 Obital Motion Using otational velocity, we see that the squae of the peiod is popotional to the cube of the distance between the two masses v v 4 T GM T GM T 4 3 GM

35 Obital Motion Fom this we can develop a elationship between the obits of two planets obiting aound the same cental body (like the planets in ou sola system obiting the sun) T T T T 3 GM GM 3

36 Keple and His Thee Laws of Motion

37 Undestandings: Newton s law of gavitation Gavitational field stength

38 Data Booklet Refeence: Mm F G F g m M g G

39 Applications And Skills: Descibing the elationship between gavitational foce and centipetal foce Applying Newton s law of gavitation to the motion of an object in cicula obit aound a point mass

40 Applications And Skills: Solving poblems involving gavitational foce, gavitational field stength, obital speed and obital peiod Detemining the esultant gavitational field stength due to two bodies

41 Essential Idea: The Newtonian idea of gavitational foce acting between two spheical bodies and the laws of mechanics ceate a model that can be used to calculate the motion of planets.

42 QUESTIONS?

43 Homewok #15-5

DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS TSOKOS LESSON 10-1 DESCRIBING FIELDS Essential Idea: Electic chages and masses each influence the space aound them and that influence can be epesented