Free Fall Physics: Identifying Constant Quantities
Understanding the motion of an object in free fall near the Earth's surface involves analyzing how different physical quantities behave when air resistance is ignored. Let's examine the options:
Analysis of Options:
- Energy: While the total mechanical energy (potential + kinetic) remains constant in ideal free fall, the question asks for *a* physical quantity. Energy is a broader concept, and its components (kinetic and potential) are constantly interchanging.
- Momentum: Momentum is defined as the product of mass and velocity ($p = mv$). Since the velocity ($v$) of the object changes continuously due to acceleration during free fall, its momentum also changes. Therefore, momentum is not constant.
- Acceleration due to gravity ($g$): Near the Earth's surface, the acceleration due to gravity is considered a constant value, approximately $9.8 \, \text{m/s}^2$. This acceleration is independent of the object's mass and properties (neglecting air resistance). It dictates the rate at which the object's velocity changes.
- Velocity: Velocity is a vector quantity representing speed and direction. In free fall, the object's speed increases due to the constant acceleration, meaning its velocity is constantly changing. Therefore, velocity is not constant.
Conclusion on Constant Quantity:
Neglecting air resistance, the primary factor governing the motion of an object in free fall near the Earth's surface is the acceleration due to gravity. This acceleration, denoted by $g$, remains constant throughout the fall.
Correct Option: 3. Acceleration due to gravity remains constant.
Important Questions from Gravity
Who among the following was the first to conclude that in vacuum all objects fall with the same acceleration g and reach the ground at the same time?
Who among the following is credited with postulating three laws of planetary motion?
When did Henry Cavendish report the measurement of the gravitational constant with the mass and density of the Earth?
Which of the following law states that, "The force between two objects is directly proportional to the product of their masses?"
Which of the following statements about the movement of planets is true?
A. A planet's orbit is elliptical with the Sun at one of two focal points.
B. The orbit of a planet is circular with the sun in the center.
C. The orbit of a planet is elliptical with another planet in one of the two center-points.
D. The orbit of a planet is circular with another planet in the center.
