Write-Up for Lab 10.1: Falling in a Gravitational Field
PHYS121 Week 3

For this lab you will drop several objects from the same height and observe how they fall and how long each takes to hit the ground. Consider the following as you complete the lab and answer the Write-Up Questions below: * Do the objects fall at the same rate? * What if the objects are different sizes, does that make a difference?

Questions:

1. The acceleration due to gravity calculated this way works well for objects near the Earth’s surface. How would you have to change the above equation if the object was 100,000 meters above the ground?

(Note: this question refers to Newton’s equation for the force of gravity between two objects. How would that change if the radius of the earth or distance were increased by 100,000 meters. To help you answer this question, please review your textbook, chapter 3, Newton’s law of Gravitation section.)

F= (6.67 x10-11N.m2/kg2)(m1)(m2)
100,0002
G is inversely proportional to the square of the distance from the center of the earth.

100 km above the earth's surface, g is reduced by a factor [6370/ (6370+100)] ^2 = 0.969
That would make it 9.51 m/s^2

6370 km is the radius of the earth.

For questions 2 and 3, please consult the textbook and additional research materials on Newton’s Second Law of Motion. Pay particular attention to mass, gravity, acceleration and how they inter-relate.

2. How does air resistance alter the way we perceive falling objects?

As a falling object accelerates through air, its speed increases and air resistance increases. While gravity pulls the object down, we find that air resistance is trying to limit the object's speed. Air resistance reduces the acceleration of a falling object. It would accelerate faster if it was falling in a vacuum.

Neglecting air resistance, the velocity of a falling object increases 9.81 m/s each second.
Neglecting air resistance, we would see the object going faster and faster, with no limit.

With air resistance:
The force of air resistance causes the object to decelerate as it falls.

Newton’s 2nd law states that the sum of the forces equals the mass times acceleration.

3. Is the force acting on a massive object larger than that acting on a less massive one? How can you verify this without taking any measurements?

If the force is gravity, the answer is yes. Gravity "pulls" on an object in proportion to its mass. A heavier (more massive) object is pulled on by gravity more than a lighter (less massive) object.