## 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 ### 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 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 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

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?