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Transcript
STARTER • Galileo Galilei was an Italian physicist, mathematician, engineer, astronomer, and philosopher who played a major role in the scientific revolution. • He proposed that all falling bodies/objects accelerate uniformly. • Meaning if I dropped a bowling ball and a golf ball from the rooftop they will hit the earth at the same time. • Is this true? Why or why not? GRAVITY, AIR RESISTANCE AND TERMINAL VELOCITY DAY 19 MINI-LAB • Questions • Pre-Lab Questions 1.If you drop the two objects from the same height, will they hit the floor at the same time? 2.Does the mass or weight of the object have an effect on how fast the object falls? MINI-LAB • Questions • Post-Lab Questions 1.What does gravity mean to you? 2.Is gravity a weak force or a small force? Think before you answer? 3.How do you know that there is gravity on Earth? SOME BASICS… DRAW A PICTURE ALONG WITH EACH FACT TO HELP YOU REMEMBER IT! • An object’s mass _______ affect the acceleration of the Won’t object due to gravity on earth. opposite • Friction always acts in the _________ direction as motion. surface area • The ___________ of an object will affect the velocity of a free falling object dropping towards earth. WHAT IS GRAVITY? • Gravity is NOT “the force that pulls you down!” • Gravity attracts all objects with mass inward towards other objects with mass. THE FORCE OF GRAVITY • What is the force of gravity? • The force of gravity is NOT the same as the acceleration DUE to gravity! FREE FALL • Objects whose only acceleration is due to gravity are in free fall. • Theoretically, objects in free fall continue to accelerate as long as they are falling. • All free falling objects accelerate at the same rate regardless of their mass. (9.8 m/s2) GALILEO'S FAMOUS EXPERIMENT ACCELERATION OF GRAVITY • Any object which is being acted upon only by the force of gravity is said to be in a state of free fall. There are two important motion characteristics which are true of free-falling objects: • Free-falling objects do not encounter air resistance. • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s2 (often approximated as 10 m/s2) FREE FALL • Newton’s 2nd Law predicts this! •𝑎= 𝐹 𝑚 • The force of gravity felt by a more massive object is greater AIR RESISTANCE • Air resistance is an upward force exerted on an object as it falls by air • It is, in essence, a frictional force • For simplicity, the amount of air resistance is determined by two factors • The cross-sectional area of the object • The speed of the object TERMINAL VELOCITY Determine the acceleration of this 85 kg skydiver at points A-D. (Hint: F=ma) 9.8 m/s2 5.68 m/s2 1.56 m/s2 0 m/s2 TERMINAL VELOCITY • The terminal velocity of a skydiver in a free-fall position with a semi-closed parachute is about 195 km/hr. • Higher speeds can be attained if the skydiver pulls in his limbs. In this case, the terminal velocity increases to about 320 km/hr! • The more compact and dense the object, the higher its terminal velocity will be. QUESTIONS • What factor causes terminal velocity to occur? • If an object is at terminal velocity, is it speeding up, slowing down, or falling at a constant speed? • Describe and explain how forces change on a falling object. TERMINAL VELOCITY Consider a skydiver: 1) At the start of his jump the air resistance accelerates downwards. zero is _______ so he ________ 2) As his speed increases his air resistance will _______ increase 3) Eventually the air resistance will be big balance the skydiver’s weight. enough to _______ At this point the forces are balanced so constant - this is his speed becomes ________ called TERMINAL VELOCITY How the forces change with time. KEY Gravity (constant value & always present…weight) Air resistance (friction) Net force (acceleration OR changing velocity) TERMINAL VELOCITY Consider a skydiver: 4) When he opens his parachute the air resistance suddenly increases ________, causing him to start slowing____. down _____ 5) Because he is slowing down his air decrease resistance will _______ until it weight balances his _________. The skydiver has now reached a new, terminal velocity lower ________ _______. EXIT SLIP • Must turn in lab! • With questions answered correctly.