4 Some basics… Draw a picture along with each fact to help you remember it! An object’s mass _______ affect the acceleration of the object due to gravity on earth.Friction always acts in the _________ direction as motion.The ___________ of an object will affect the velocity of a free falling object dropping towards earth.Won’toppositesurface area
5 What IS gravity? Gravity is NOT “the force that pulls you down!” Gravity attracts all objects with mass inward towards other objects with mass.
6 Newton’s Universal Law of Gravitation Each and every object in this universe there is the force of attraction between them which is called gravitation force that is always directly proportion to the masses and indirectly proportion to the square of the distance between them
7 the Force of Gravity What is the force of gravity? The force of gravity is NOT the same as the acceleration DUE to gravity!
8 Free FallObjects whose only acceleration is due to gravity are in free fall.All free falling objects accelerate at the same rate regardless of their mass. (9.8 m/s2)
10 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/s/s (often approximated as 10 m/s/s)
11 Free Fall Newton’s 2nd Law predicts this! a = F m The force of gravity felt by a more massive object is greater
13 Air ResistanceAir resistance is an upward force exerted on an object as it falls by airIt is, a frictional force
14 Terminal VelocityDetermine the acceleration of this 85 kg skydiver at points A-D. (Hint: F=ma)9.8 m/s25.68 m/s21.56 m/s20 m/s2
15 Terminal VelocityThe terminal velocity of a skydiver in a free-fall position with a semi-closed parachute is about 195 km/hHigher speeds can be attained if the skydiver pulls in his limbs. In this case, the terminal velocity increases to about 320 km/h!
16 Possible Test 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.
17 Terminal Velocity Consider a skydiver: At the start of his jump the air resistance is _______ so he____ downwards.zeroaccelerates2) As his speed increases his air resistance will _______increase3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITYbalanceconstant
18 How the forces change with time. KEYGravity(constant value & always present…weight)Air resistance(friction)Net force(acceleration OR changing velocity)
19 Terminal Velocity Consider a skydiver: 4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____.increasesslowing down5) Because he is slowing down his air resistance will _______ until it balances his _________. The skydiver has now reached a new, lower ________ _______.decreaseweightterminal velocity
20 Velocity-time graph for the sky diver Parachute opens – diver slows downVelocitySpeed increases…Terminal velocity reached…On the MoonDiver hits the groundNew, lower terminal velocity reachedTime
21 Projectile MotionProjectile: When a falling object also experiences horizontal motionHorizontal motion does not affect vertical motion