Kickoff
In your notes…
1. Net force = 350 N
2. Mass = 60 kg
Mass = 70 kg
Acceleration = 3.5
Acceleration = ?
Net force = ?
3. Net force = 240 N
Acceleration = 1.6
Mass = ?
𝑚
𝑠2
𝑚
𝑠2
5.2 Weight and Terminal
Velocity
Objectives:
1. Distinguish between weight and mass, and convert
between them.
2. Explain how air resistance causes terminal velocity of
falling objects
Weight vs Mass
Weight
Mass
A downward force from gravity
Not a force
Measured with a spring scale
Measured with a balance
Unit: Newtons
Unit: Kilograms
Depends on location
(earth vs moon)
Is the same everywhere
(Even with no gravity)
Weight Vs Mass
Acc. of gravity on Earth:
𝑔 = −9.8
Find Weight by multiplying:
𝐹𝑔 = 𝑚 ∙ 𝑔
Find Mass by dividing:
𝑚=
𝐹𝑔
𝑔
𝑚
𝑠2
Weight Vs Mass
Buzz Aldrin weighs 1100 N on earth. What is his mass?
The acc. of gravity on the moon:
𝑔 = −1.622
What is Buzz’s weight on the moon?
𝑚
𝑠2
Weight Vs Mass
Buzz Lightyear has crash landed onto an alien planet. His bathroom
scale says he weighs 60.8 N and his mass is 3.2 kg.
What is the acceleration due to gravity?
Would he weigh more or less on earth?
𝑔=
𝐹𝑔
𝑚
Terminal velocity
When an object begins to
fall:
Speed:
++
Air resistance: ++
Net Force:
--
When an object begins to fall, the speed increases.
As the speed increases, the air resistance gets
bigger.
As the air resistance gets bigger, the net force gets
smaller
Acceleration:
--
As the net force gets smaller, the acceleration gets
smaller
Net force:
=0
Eventually, the air resistance will equal the weight
and net force will be zero.
Acceleration:
=0
The object will stop accelerating and will fall at a
constant speed.
Terminal velocity
The constant speed when air resistance
equals weight is called Terminal Velocity
Terminal Velocity
Which will have a higher terminal velocity: A
lightweight tennis ball or a heavy shot put? Why?
Why do skydivers fall slower when they spread
their arms and legs outwards?
Would a tennis ball dropped from the top of a
skyscraper be more dangerous than one dropped
from the middle?
Describe what happens to terminal velocity when
a parachute is opened.
Practice Problems
Chapter 5 #9-23