Essay by chao2410High School, 12th gradeB, March 2004

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Projectile Motion

*Object, moving in gravitational field, with gravity only force acting on it - moves in a parabolic shape

*Measured in two independent dimensions

oVertical - gravity effects

oHorizontal - remains constant though-out motion

*Galileo - formulas for projectile motion

oS = UT - Horizontal motion

oS = UT + ½ AT2 - Vertical motion

Galileo analysis of Projectile motion

*Trajectory of projectile makes a parabolic shape

*Led him to consider reference frames

*Opponent believed in idea of geocentrism - stone would be left behind if Heliocentric

*Galileo explained - didn't fall away because shared the earths motion

oTower and stone shared the same horizontal velocity

oExperiment - dropped object from crows nest of ship - dropped down to base of tower whether stationary or moving at a constant velocity

*This led to Galilean relativity

o'The laws of mechanics are the same in a frame of reference that is at rest or one that is moving at a constant velocity'

Escape Velocity

*The necessary velocity needed to leave the earths surface

*Depends on gravitational acceleration of planet - hence mass and diameter of planet

*~11.2 km/sec on earth - not taking into account atmospheric friction

*Lower escape velocity - least likely planet has atmosphere

Newton and Escape Velocity

*Proposed the idea of artificial satellites

*Projectile launched horizontally from mountain -

oAs launch velocity increased, object would go further till crashing or till it follows ellipse of earth - orbit

Circular motion

*Motion of an object in circular path, with constant speed - uniform circular motion

*Speed same - however changing velocity and accelerating - direction always changing

*Change in velocity - directed towards centre of circle; centripetal force

*Uniform circular motion - centripetal force is always towards centre of circle

*Ac = MV2/R

*Orbit is acquired by lifting...