Falling Objects
Falling Objects
How do objects travel as they fall?
Prior to mid-1600’s people believed that objects stayed at a constant velocity as they fell and that this velocity depended on the mass
Galileo challenged this belief
He suggested that all objects (regardless of mass) accelerate at the same constant rate in the absence of air resistance
Through experiment, showed that the distance traveled is directly proportional to the square of time
In the absence of air all objects have the same acceleration
For objects with a small mass and large surface area, air resistance plays a major roll
For ordinary objects, air resistance is negligible
No air resistance Air resistance
Acceleration due to Gravity
Acceleration of falling objects is due to gravity’s pull on them
Greater the gravity, greater the acceleration produced
The value of acceleration due to gravity varies slightly with the elevation and latitude but not enough to matter
Gravity on Earth
Average acceleration on earth g = -9.8 m/s 2
Always a negative number because gravity is always pulling down
– even if the object is moving up
Question
Where would a rock accelerate at the greatest rate: the earth or the moon?
Graphically
Motion Equations with Falling
Objects
Substitute g for a and y for x
Since gravity pulling down, use g = - 9.8 m/s 2
Ex. 1
A ball is dropped from a 70.0 m high tower. How far will it have fallen after
3.00s?
Ex. 2
A ball is thrown down a 70.0 m tower with an initial velocity of 3.00 m/s. How far will it travel after 2.00 s? What will its speed be?
Ex. 3
A ball is thrown up into the air at 15 m/s.
How high will it go? How long before it comes back to his hand?
Ex. 4
For the ball in the previous problem. A) how long does it take the ball to reach the max height B) what is the velocity when it hits his hand? C) at what time is the ball 8.00 m above his hand?
