What is the difference between an object falling in a vacuum versus an object falling in air?

In a vacuum, there is no air resistance, so the object accelerates at a constant rate ($g$) indefinitely. In air, air resistance increases with speed until it balances the weight, resulting in a constant terminal velocity.

How does the acceleration of a falling object change as it approaches terminal velocity?

The acceleration decreases over time. As the object speeds up, air resistance increases, which reduces the resultant downward force ($F = W - D$), thereby reducing the acceleration ($a = F/m$) until it reaches zero.

When an object is at terminal velocity, which is greater: Weight or Air Resistance?

Neither; they are equal in magnitude but opposite in direction. Because the forces are balanced, the resultant force is zero, which is the requirement for the object to maintain a constant velocity.

What is a common mistake when naming the downward force acting on a falling skydiver?

A common mistake is calling the force 'gravity'. In physics, the force exerted by gravity on an object's mass is specifically called 'Weight'.

Why is it incorrect to say that an object at terminal velocity has 'stopped'?

Terminal velocity is the *fastest* speed an object reaches during its fall. While the *acceleration* has stopped (it is zero), the object is still moving downwards at a high, constant speed.

What happens to the weight of an object as its speed increases during a fall?

The weight remains constant because it only depends on the object's mass and the gravitational field strength ($W = mg$), neither of which change significantly during the fall.

Define Terminal Velocity.

Terminal velocity is the constant maximum velocity reached by an object falling through a fluid when the upward drag force equals the downward weight force.

What is the formula for Weight, and what do the variables represent?

The formula is $W = mg$, where $W$ is the weight in Newtons (N), $m$ is the mass in kilograms (kg), and $g$ is the gravitational field strength (approx. $10 \text{ N/kg}$ on Earth).

What is the resultant force on an object moving at terminal velocity?

The resultant force is zero Newtons ($0 \text{ N}$). This is because the upward air resistance and downward weight are perfectly balanced.

Why does air resistance increase as an object falls faster?

As the object's speed increases, it collides with more air particles per second and with greater force. These collisions create the resistive drag force that opposes motion.

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Double Award / Physics

1. Forces & Motion

Terminal Velocity

Summary

Terminal velocity is the constant maximum speed achieved by an object falling through a fluid (gas or liquid). It occurs when the downward force of gravity is exactly balanced by the upward resistive force of drag, resulting in zero net force and zero acceleration.

1. Definition & Core Concepts

Terminal Velocity is defined as the steady, constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.
When an object moves through a fluid like air, it experiences Air Resistance (or drag), which is a frictional force that opposes the motion of the object.
The state of terminal velocity represents a dynamic equilibrium where the Resultant Force acting on the object is zero, meaning the object continues to move at a constant velocity according to Newton's First Law.

Diagram of an object at terminal velocity showing equal and opposite force arrows for Weight and Air Resistance.

2. Underlying Principles

3. The Process of Reaching Terminal Velocity

Initial Phase: At the moment of release, the velocity is zero, so air resistance is zero. The resultant force is equal to the weight, and the object accelerates downwards at the maximum rate ( $g$ ).
Acceleration Phase: As the object gains speed, air resistance begins to act upwards. The net downward force ( $W - \text{Drag}$ ) becomes smaller, so the acceleration decreases, though the object is still getting faster.
Terminal Phase: Eventually, the speed becomes high enough that the upward air resistance exactly equals the downward weight. At this point, the resultant force is zero, acceleration stops, and the object maintains a constant speed.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions