Air Resistance

Learn about air resistance and terminal velocity. A frictional force caused by air particles while an object travels through the air.

Terminal Velocity

Air is made up of molecules and as a particle accelerates these particles are hit at an increasing rate.  Air resistance builds up until Fair = -Fw. At this point an object has terminal velocity.

At Terminal Velocity:

  • Fair = Fw (No net force)
  • No acceleration
  • Constant Velocity

Terminal velocity depends on the shape of an object(Aerodynamics).  Terminal velocity is around 53 m/s or 122 mph for a human skydiver

Air Resistance

Finding Acceleration with Air Resistance

Note: Unless a problem states there is air resistance assume none and g= 9.8 m/s2.

Until terminal velocity acceleration will be decreasing from 9.8 m/s2 until 0 m/s2

You can calculate the new acceleration by

  1. Finding the net force
  2. If you have weight but not mass calculate it using the equation: Fw = mg (air resistance does not affect an objects weight)
  3. Using the mass and the equation: Fnet = ma

Air Resistance Questions:

1. Draw a force diagram of an object with a weight of 300 N when 100 N of air resistance is encountered?

Inside the rounded square below is a force diagram with the overall net on the outside

Air Resistance Net Force

2. What is the acceleration of an object with a weight of 300 N when 100 N of air resistance is encountered?

Weight is down and air resistance is up or in the reverse direction of motion. 

Note: down is positive in my solution

 

First find the net force:

Fnet = sum of forces = 300 + (-100) = 200 N down

Next determine the mass from the weight(FW):

Fw = mg

m = Fw / g

m = 300 / 9.8

m = 30.6 kg

Lastly determine the acceleration produced by net force:

net = ma

a = Fnet / m

a = 200/ 30.6

a = 6.5 m/sdown

3. Draw a force diagram of a 40 kg object that encounters 60 N of air resistance?

First Find The weight (FW) to place in the force diagram.

FW = mg

FW = (40)(9.8) = 392 N down

Inside the rounded square below is a force diagram with the overall net on the outside

Weight is down and air resistance is up or in the reverse direction of motion

Air Resistance Net Force

4. What is the acceleration of a 40 kg object that encounters 60 N of air resistance?

FW = mg

FW = (40)(9.8) = 392 N down

 

Fnet = sum of forces = 392 + (-60) = 332N down

 

net = ma

a = Fnet / m

a = 332 / 40

a = 8.3 m/s2 down

(Click Here All Problems With Their Solutions)

Air Resistance and Terminal Velocity Quiz

1 / 8

What is the acceleration of a 1400 N skydiver at terminal velocity?

2 / 8

What is the weight of a 1400 N skydiver at terminal velocity?

3 / 8

What is the air resistance force on a 1400 N skydiver at terminal velocity?

4 / 8

What is net force of a 1400 N skydiver at terminal velocity?

5 / 8

What is the acceleration of a 1400 N  skydiver when she encounters 600 N of air resistance?  (use g = 9.8 m/s/s)

6 / 8

What is the mass of a 1400 N  skydiver when she encounters 600 N of air resistance?  (use g = 9.8 m/s/s)

7 / 8

What is the net force when a 1400 N skydiver encounters 600 N of air resistance?

8 / 8

What is the acceleration of a 1400 N skydiver that has no air resistance?

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