1 / 16

Quiz 1

Quiz 1. Each quiz sheet has a different 5-digit symmetric number which must be filled in (as shown on the transparency, but NOT the same one!!!!!) Please hand in both the exam and the answer sheets with your name on both Question/answer sheets will be handed back on Wednesday after class

ovidio
Download Presentation

Quiz 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Quiz 1 • Each quiz sheet has a different 5-digit symmetric number which must be filled in (as shown on the transparency, but NOT the same one!!!!!) • Please hand in both the exam and the answer sheets with your name on both • Question/answer sheets will be handed back on Wednesday after class • Please remain seated until we begin collecting (20-25 minutes after start) • Class after quiz

  2. Newton – Three Laws of Motion • Inertia • F = ma • Action = Reaction

  3. Newton’s Laws of Motion • Law of Inertia: A body continues in state of rest or motion unless acted on by an external force; Mass is a measure of inertia • Law of Acceleration: For a given mass m, the acceleration is proportional to the force applied F = m a • Law of Action equals Reaction: For every action there is an equal and opposite reaction; momemtum (mass x velocity) is conserved

  4. Velocity, Speed, Acceleration • Velocity implies both speed and direction; speed may be constant but direction could be changing, and hence accelerating • Acceleration implies change in speed or direction or both • For example, stone on a string being whirled around at constant speed; direction is constantly changing therefore requires force

  5. Ball Swung around on a String: Same Speed, (in uniform circular motion) Changing Direction (swinging around the circle)

  6. Acceleration Force Donut Swung around on a String

  7. Conservation of momemtum:action equal reaction • The momemtum (mv) is conserved before and after an event • Rocket and ignited gases: M(rocket) x V(rocket) = m(gases) x v(gases) • Two billiard balls: m1 v1 + m2 v2 = m1 v1’ + m2 v2’ v1,v2 – velocities before collision v1’,v2’ – velocities after collision • Example – you and your friend (twice as heavy) on ice!

  8. Force = (apple’s mass)  (acceleration due to gravity) Action = Reaction Equal and Opposite Force from the Table Net Force is Zero, No Net Motion

  9. Acceleration due to gravity • Acceleration is rate of change of velocity, speed or direction of motion, with time  a = v/t • Acceleration due to Earth’s gravity : a  g g = 9.8 m per second per second, or 32 ft/sec2 • Speed in free-fall T (sec) v (m/sec) v (ft/sec) 0 0 0 1 9.8 32 2 19.6 64 3 29.4 96 60 mi/hr = 88 ft/sec (between 2 and 3 seconds)

  10. Galileo’s experiment revisited • What is your weight and mass ? • Weight W is the force of gravity acting on a mass m causing acceleration g • Using F = m a, and the Law of Gravitation W = m g = G (m MEarth) /R2 (R – Radius of the Earth) The mass m of the falling object cancels out and does not matter; therefore all objects fall at the same rate or acceleration g = GM / R2 i.e. constant acceleration due to gravity 9.8 m/sec2

  11. Galileo’s experiment on gravity • Galileo surmised that time differences between freely falling objects may be too small for human eye to discern • Therefore he used inclined planes to slow down the acceleration due to gravity and monitor the time more accurately v Changing the angle of the incline changes the velocity v

  12. ‘g’ on the Moon g(Moon) = G M(Moon) / R(Moon)2 G = 6.67 x 10-11 newton-meter2/kg2 M(Moon) = 7.349 x 1022 Kg R(Moon) = 1738 Km g (Moon) = 1.62 m/sec/sec About 1/6 of g(Earth); objects on the Moon fall at a rate six times slower than on the Earth

  13. Escape Velocity and Energy • To escape earth’s gravity an object must have (kinetic) energy equal to the gravitational (potential) energy of the earth • Kinetic energy due to motion K.E. = ½ m v2 • Potential energy due to position and force P.E. = G m M(Earth) / R (note the similarity with the Law of Gravitation) • Minimum energy needed for escape: K.E. = P.E. ½ m v2 = G m M / R Note that the mass m cancels out, and • v (esc) = 11 km/sec = 7 mi/sec = 25000 mi/hr The escape velocity is the same for all objects of mass m

  14. Object in orbit  Continuous fall ! Object falls towards the earth at the same rate as the earth curves away from it

More Related