Acceleration of a Falling Object

When a Falling Object Accelerates Only Due to Gravity, We Call This….

Knowing What We Know Now Why does a brick with twice the amount of mass as another brick not fall twice as fast? mass 2 mass

Well This is Confusing The greater the mass of an object, the greater is the gravitational force of attraction between it and earth, So why doesn’t the brick with double the mass move to earth twice as fast?

Remember Inertia! Acceleration of an object depends not only on the force (in this case mass), but also on the object’s resistance to motion – inertia Inertia is a resistance to acceleration

So twice the force exerted on twice the inertia produces the same acceleration as half the force exerted on half the inertia mass 2 mass F --- = g m 2F --- = g 2m

So acceleration of a free falling object is independent of an object’s mass A boulder 100 times more massive than a pebble falls with the same acceleration. Although the force on the boulder is 100 time greater, its resistance to change (inertia) is 100 times that of the pebble

Okay Take That All In….

When Acceleration is Less Than g Nonfree Fall

Not in a Vacuum In a vacuum, the net force is the weight because it is the only force. In the presence of air resistance, however, the net force is less than the weight – it is the weight minus air drag (the force arising from air resistance)

The force of air drag of a falling object depends on 2 things: 1.The frontal area of the falling object - the amount of air the object must plow through as it falls 2.The speed of the falling object - the greater the speed, the greater the number of air molecules an object encounters per second, and the greater the force of molecular impact

A Falling Feather Air drag greatly affects feathers as they fall Because a feather has so much area for an object so light in weight, it doesn’t have to fall very fast before the upward acting air resistance cancels the downward –acting weight. The net force on the feather is then 0 and acceleration terminates When acceleration terminates we say the object has reached its terminal speed

Skydiving As a falling skydiver gains speed, air drag may finally build up until it equals the weight of the skydiver If and when this happens, the net force becomes zero and the skydiver no longer accelerates – reaching terminal velocity For a skydiver this is about 200 km/h A smaller terminal velocity may be obtained by spreading out like a flying squirrel

Skydiving The large frontal area provided by a parachute produces low terminal speeds for safe landings **Read last paragraph of pg. 59

Problem Nellie Newton skydives from a high flying helicopter. As she falls faster and faster through the air, does her acceleration increase, decrease, or remain the same? a= mg-R/m As R increases, a decreases If she falls fast enough so that R=mg then a =0 she will have no acceleration and fall at a constant speed

Terminal Velocity Terminal Velocity Video

Practice Review questions pg. 61 #27-35 Ranking pg.63 #4 Exercises pg. 64 #33, 36, 41-54