Gravity Air Resistance Terminal Velocity and Projectile Motion

Gravity, Air Resistance, Terminal Velocity, and Projectile Motion A Whole Bunch of Ideas in one Show

Science Standard n a. b. S 8 P 3. Students will investigate relationship between force, mass, and the motion of objects. Determine the relationship between velocity and acceleration. Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

Enduring Understanding n Acceleration of an object is dependent upon the mass of the object and the size and direction of the unbalanced force.

Essential Question n How does Gravity affect Acceleration?

Some basics… Draw a picture along with each fact to help you remember it! Won’t An object’s mass _______ affect the acceleration of the object due to gravity on earth. opposite n Friction always acts in the _____ direction as motion. surface area n The ______ of an object will affect the velocity of a free falling object dropping towards earth. n

Vocabulary to know n n n The force that pulls an object towards another object When you throw something it is a projectile When you drop something it is in a free fall The friction involved here is air resistance Universal LAW of gravity states that the force of gravity acts on all objects in the universe

What IS gravity? Gravity is NOT “the force that pulls you down!” n Gravity attracts all objects with mass inward towards other objects with mass. n

the Force of Gravity n n 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. n Theoretically, objects in free fall continue to accelerate as long as they are falling. n All free falling objects accelerate at the same rate regardless of their mass. (9. 8 m/s 2) n

Galileo's Famous Experiment

The Acceleration of Gravity (g) n n Galileo demonstrated that g is the same for all objects, regardless of their mass! This was confirmed by the Apollo astronauts on the Moon, where there is no air resistance. © 2004 Pearson Education Inc. , publishing as Addison-Wesley

Acceleration of Gravity n 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 freefalling 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)

Acceleration from Gravity n n n n If the velocity and time for a free-falling object being dropped from a position of rest were tabulated, then one would note the following pattern. Time (s) Velocity (m/s) 0 0 1 - 9. 8 2 - 19. 6 3 - 29. 4 4 - 39. 2 5 - 49. 0 The rate of falling increases by 9. 8 m/s every second.

2 -5. Free Fall A ball thrown horizontally will fall at the same rate as a ball dropped directly.

Free Fall n Newton’s 2 nd Law predicts this! a= F m n The force of gravity felt by a more massive object is greater

2 -5. 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.

Air Resistance Air resistance is an upward force exerted on an object as it falls by air n It is, in essence, a frictional force n For simplicity, the amount of air resistance is determined by two factors n – The cross-sectional area of the object – The speed of the object

W Richa Terminal Velocity Consider a skydiver: 1) At the start of his jump the air zero so he resistance is _______ Accelerates _____downwards. 2) As his speed increases his air increase resistance will _______ 3) Eventually the air resistance will be big enough to _______ balance the skydiver’s weight. At this point the forces are balanced so his constant - this is 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 resistance will _______ decrease until it balances his _____. The weight skydiver has now reached a new, terminal _______. velocity lower ____

Velocity-time graph for the Parachute opens – Velocity sky diver slows down Speed increases… Terminal velocity reached… On oon M he t Time New, lower terminal velocity reached Diver hits the ground

Projectile Motion n n Projectile: When a falling object also experiences horizontal motion Horizontal motion does not affect vertical motion

n n All objects released at the same time (with no vertical initial velocity) will hit the ground at the same time, regardless of their horizontal velocity The horizontal velocity remains constant throughout the motion (since there is no horizontal force)