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Transcript

Free Fall The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2. Galileo found that all things fall at the same rate. Free Fall The rate of falling increases by 9.8 m/s every second. Height = ½ gt2 For example: ½ (9.8 )12 = 4.9 m ½(9.8)22 = 19.6 m ½ (9.8)32 = 44.1 m ½ (9.8)42 = 78.4 m Free Fall A ball thrown horizontally will fall at the same rate as a ball dropped directly. Free Fall A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity. When it passes the thrower, it will be traveling at the same rate at which it was thrown. Free Fall An object thrown upward at an angle to the ground follows a curved path called a parabola. Air Resistance • In air… – A stone falls faster than a feather • Air resistance affects stone less • In a vacuum – A stone and a feather will fall at the same speed. Air Resistance • Free Fall – A person in free fall reaches a terminal velocity of around 54 m/s – With a parachute, terminal velocity is only 6.3 m/s • Allows a safe landing Air Resistance • Ideal angle for a projectile – In a vacuum, maximum distance is at an angle of 45o – With air resistance (real world), angle is less • Baseball will go furthest hit at an angle of around 40o First Law of Motion The first law of motion states: If no net force acts on it, an object at rest remains at rest and an object in motion remains in motion at a constant velocity. Inertia and Mass Inertia is the apparent resistance an object offers to any change in its state of rest or motion. Second Law of Motion Newton's second law of motion states: The net force on an object equals the product of the mass and the acceleration of the object. The direction of the force is the same as that of the acceleration. F = Ma Second Law of Motion A force is any influence that can cause an object to be accelerated. 1 newton 1 N 1 (kg)(m/s 2 ) Mass and Weight • Weight Definition: The force with which an object is attracted by the earth’s gravitational pull • Example: A person weighing 160 lbs is being pulled towards the earth with a force of 160 lbs (712 N). – Near the earth’s surface, weight and mass are essentially the same Weight (mass)(acc eleration of gravity) w mg Third Law of Motion The third law of motion states: When one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object. Third Law of Motion Examples of the 3rd Law Circular Motion Centripetal force is the inward force exerted on an object to keep it moving in a curved path. Centrifugal force is the outward force exerted on the object that makes it want to fly off into space. Circular Motion Circular Motion 833 N is needed to make this turn. If he goes too fast, which wheels are likely to come off the ground first? Artificial Satellites • The world's first artificial satellite was Sputnik I, launched in 1957 by the Soviet Union. GPS-Global Positioning Satellite Artificial Satellites The escape speed is the speed required by an object to leave the gravitational influence of an astronomical body; for earth this speed is about 40,000 km/h.