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Terminal velocity

 

Free fall


The two main forces that act upon an object that is falling are weight and air resistance.

 

The image shows the concept of free fall, showing a skydiver in mid-air and the forces acting on them, including air resistance and weight.

 

An object’s weight remains the same throughout a fall. The objects weight is the force of caused by the mass being acted on it by Earth's gravity.


Air resistance is a frictional force that slows down the object’s motion. But in a vacuum, there is no air resistance. A falling object speeds up at first. The more speed it has, the more air resistance it faces.

 

Terminal velocity


Terminal velocity is the maximum speed of an object when it falls freely through a gas or liquid. At this speed, the object stops accelerating because the forces on it are equal. For example, a skydiver who jumps out of a plane starts speeding up because their weight is greater than the air resistance. But as they go faster, the air resistance also increases until it matches their weight, so they stop getting faster. This is their terminal velocity.

 

This image illustrates a skydiver in mid-air, with annotations indicating the forces acting on them. The skydiver’s face is obscured for privacy. A plane is visible in the background, indicating that the skydiver has recently jumped. The annotations are: Air resistance with an upward arrow indicates the force counteracting gravity. Weight with a downward arrow represents gravitational pull on the skydiver. Resulting force = 0 suggests that air resistance and weight are balanced. This means that the skydiver is in a state of terminal velocity, where they fall at a constant speed. The skydiver can change their terminal velocity by changing their body position, which affects the amount of air resistance they experience.

 

The mass and the shape of an object falling through a fluid affect how fast it can go.


Terminal velocity is affected by two main factors:

 

  • Mass
  • Shape of the object

 

The more mass the object has, the more weight it has.


Objects that have big surface areas face a lot of air resistance when they move. These objects are said to be less aerodynamic.

 

High terminal velocity

Low terminal velocity

Smaller surface area = lower air resistance.

For example, a skydiver has a small surface area that makes little air resistance. Because of this, the skydiver is able to reach a high terminal velocity.

 

Larger surface area = higher air resistance.

For example, a parachutist who opens their parachute has a big surface area that makes a lot of air resistance. Because of this, the parachutist is able to reach a lower terminal velocity.

Image shows that if a skydiver has a small surface area they make little air resistance.

Image shows a that when parachutist opens their parachute they have a big surface area that makes a lot of air resistance.

 

How to describe the motion of a falling object


What happens as a parachutist jumps out of a plane, freefalls, and then opens their parachute?

 

How to describe the motion of a falling object


What happens as a parachutist jumps out of a plane, freefalls, and then opens their parachute?

 

A skydiver jumps out of an aeroplane and begins to accelerate.

As the skydiver continues to accelerate, the air resistance increases.
This image illustrates a skydiver in mid-air, with labels and arrows indicating the forces acting on them. A plane is visible in the background, indicating that the skydiver has recently jumped. The labels are: Air resistance with an upward arrow indicates the force counteracting gravity. Weight with a downward arrow represents gravitational pull on the skydiver. Larger resulting force with a diagonal downward arrow shows the net force on the skydiver. This means that the skydiver is in a state of free fall, where they accelerate downwards due to gravity. The skydiver can reduce their acceleration by increasing their air resistance, which depends on their body position and surface area. This image illustrates a skydiver in mid-air, with labels and arrows indicating the forces acting on them. A plane is visible in the background, indicating that the skydiver has recently jumped. The labels are: Air resistance with an upward arrow indicates the force counteracting gravity. Weight with a downward arrow represents gravitational pull on the skydiver. Smaller resulting force with a diagonal downward arrow shows the net force on the skydiver. This means that the skydiver is in a state of free fall, where they accelerate downwards due to gravity. The skydiver can reduce their acceleration by increasing their air resistance, which depends on their body position and surface area.

 


The skydiver reaches ‘terminal velocity’ The weight and air resistance are the same.

As the skydiver pulls their parachute, the surface area is drastically increased. This increases the air resistance and slows the skydiver down.
This image illustrates a skydiver in mid-air, with annotations indicating the forces acting on them. The skydiver’s face is obscured for privacy. A plane is visible in the background, indicating that the skydiver has recently jumped. The annotations are: Air resistance with an upward arrow indicates the force counteracting gravity. Weight with a downward arrow represents gravitational pull on the skydiver. Resulting force = 0 suggests that air resistance and weight are balanced. This means that the skydiver is in a state of terminal velocity, where they fall at a constant speed. The skydiver can change their terminal velocity by changing their body position, which affects the amount of air resistance they experience. This image is a diagram illustrating the forces acting on a parachutist. The parachutist is depicted mid-air with labels indicating “Air resistance” upwards, “Weight” downwards, and “Largest resulting force” downwards. The labels are: Air resistance with an upward arrow indicates the force counteracting gravity. Weight with a downward arrow represents gravitational pull on the parachutist. Largest resulting force with a diagonal downward arrow shows the net force on the parachutist. This means that the parachutist is in a state of acceleration, where they speed up downwards due to gravity. The parachutist can reduce their acceleration by increasing their air resistance, which depends on the size and shape of their parachute.

 

As the skydiver is starts to decelerate, the air resistance decreases.

The skydiver has now reached a low terminal velocity. This terminal velocity is much lower than the one before the parachute was opened.
This image is a diagram illustrating the forces acting on a parachutist. The parachutist is depicted mid-air with labels indicating “Air resistance” upwards, “Weight” downwards, and “Largest resulting force” downwards. This image is a diagram illustrating the forces acting on a parachutist. The parachutist is depicted mid-air with labels indicating “Air resistance” upwards, “Weight” downwards, and “Largest resulting force” downwards.

 

 

Summary:

 

  • Weight and air resistance are the two main forces on a falling object.
  • A falling object can reach terminal velocity, this is the maximum speed it can go when the forces are equal.

 

 

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