GCSE Physics - Terminal Velocity

Summary

In this video, we explore why falling objects reach terminal velocity, where their speed stabilizes and they stop accelerating. The video begins by explaining the forces acting on a person jumping out of an airplane, including gravity (weight) and air resistance. As the person falls, air resistance increases, slowing their acceleration until it equals the weight, at which point terminal velocity is reached. The concept of terminal velocity is further explained with the example of a parachute, which increases air resistance and lowers the terminal velocity. The video concludes with a recap of the key points discussed.

Takeaways

• 😀 The concept of terminal velocity refers to the point at which an object's velocity becomes constant because the forces acting on it balance out.
• 😀 When a person first steps out of an airplane, the only force acting on them is their weight, causing them to accelerate downward.
• 😀 Air resistance, also known as drag, acts in the opposite direction to weight, slowing the person down as they fall.
• 😀 The amount of air resistance depends on the person's surface area and velocity; larger surface areas and higher velocities result in more collisions with air particles.
• 😀 As the person falls and gains speed, the air resistance increases, reducing the net force acting on them, causing a decrease in acceleration.
• 😀 The velocity-time graph shows a decreasing slope as acceleration slows down due to increasing air resistance.
• 😀 Terminal velocity occurs when air resistance equals the person's weight, resulting in no net force and no further acceleration.
• 😀 If the person opens a parachute, their surface area increases significantly, causing a dramatic increase in air resistance.
• 😀 After opening the parachute, the person decelerates and eventually reaches a new, lower terminal velocity due to the higher air resistance.
• 😀 The new terminal velocity with the parachute is slower than the initial terminal velocity before the parachute was deployed.
• 😀 In summary, falling objects accelerate until air resistance equals weight, and at that point, they stop accelerating and maintain terminal velocity until some external change occurs.

Q & A

What happens to a person when they first step out of an airplane?

When a person first steps out of an airplane, gravity pulls them downward with a force called weight. Initially, the person is stationary and begins to fall due to this force.

What is the force of weight, and how does it act on a person falling?

Weight is the force exerted on a person due to gravity. It pulls them downward towards the Earth, and its magnitude remains constant during the fall, as long as the person's mass doesn't change.

How does air resistance affect a falling object?

Air resistance is an upward force caused by collisions between the object and air particles. It acts opposite to the force of weight, and its magnitude increases as the object's velocity increases.

What factors determine the size of air resistance acting on a falling object?

Air resistance depends on two main factors: the surface area of the object (larger surface area leads to more collisions with air particles) and the velocity of the object (faster movement leads to more collisions).

What happens to the resultant force as air resistance increases during free fall?

As air resistance increases with velocity, it starts to cancel out some of the downward force of weight. This results in a decrease in the net or resultant force, causing a reduction in the rate of acceleration.

What does a velocity-time graph look like for a falling object experiencing increasing air resistance?

The graph starts steep as the object accelerates rapidly. As time passes and air resistance increases, the graph becomes less steep, showing that acceleration is decreasing as the object approaches terminal velocity.

What is terminal velocity, and when is it reached?

Terminal velocity is the constant speed an object reaches when the force of air resistance equals the force of weight. At this point, the object stops accelerating and continues falling at a constant velocity.

What happens to a person’s fall if they open a parachute?

Opening a parachute increases the surface area of the person, which greatly increases air resistance. This causes the person to decelerate, eventually reaching a new, lower terminal velocity.

How does the terminal velocity change when a parachute is deployed?

When the parachute is deployed, the increased air resistance reduces the person's velocity. As a result, the new terminal velocity with the parachute is lower than the terminal velocity without it.

What key concept is essential for understanding terminal velocity?

The key concept is that when the forces of air resistance and weight balance each other out, the object reaches terminal velocity and will no longer accelerate, maintaining a constant velocity.