Transcript Section 7.3 Day 2

Friday, Jan. 29th
Agenda
• Collect Homework: “Isaac Newton” WS
• Finish section 7.3:
– free fall, weight, terminal velocity, Newton’s 3rd
law
• In-Class Assignment
– Integrating Space Science, pg. 238, 4 problems
• Movie: “Laws of Motion”
• Homework:
– “Gravity and the Planets” worksheet
Homework
• “The Great Plague and Isaac Newton”
• Turn in
Free Fall and Weight
Free fall: the motion of a body when only
the force of gravity is acting on it
Because free-fall acceleration results from
the force due to gravity, it is abbreviated by
the letter g.
Near Earth’s surface, g is equal to 9.8 m/s2.
Free-fall Acceleration near Earth’s
Surface is Constant
In the absence of air resistance, all objects
near Earth’s surface accelerate at the
same rate, no matter what their mass is.
This means that if you dropped a 1.5 kg
book and a 15 kg rock from the same
height, they would hit the ground at the
same moment.
Weight = mass X free-fall acceleration
The force on an object due to gravity is
called its weight.
Weight equals mass times free-fall
acceleration.
Weight = mass X free-fall acceleration
w = m·g
Weight = mass X free-fall acceleration
Because weight is a force, the SI unit for
weight is the Newton, N.
Weight is Different from Mass
Mass: the measure of the amount of matter
in an object.
Weight: the gravitational force an object
experiences due to its mass.
The weight of an object depends on gravity,
so a change in an object’s location will
change its weight.
Remember, weight = mass X g
(You will need to remember this for your in-class
assignment today)
Terminal Velocity
Terminal velocity: the maximum velocity
reached by a falling object that occurs
when the air resistance is equal to the
force of gravity.
When the air resistance = the gravitational
force, the object stops accelerating.
Terminal Velocity
The sky-diver
reaches a terminal
velocity of 320 km/hr
before he opens his
chute.
Newton’s
rd
3
Law
Newton’s Third Law: for every action
force, there is an equal and opposite
reaction force.
Forces always occur in pairs.
The action and reaction forces act on
different objects.
The action and reaction forces occur at the
same time.
Newton’s 3rd Law
The upward push on
the rocket equals the
downward push on the
exhaust gases.
Newton’s 3rd Law
According to Newton’s
third law, the soccer
ball and the foot
exert equal and
opposite forces on
one another.
In-Class Assignment
Integrating Space Science, pg. 238
Use the equation
weight = mass X g
to find the weight of a 58 kg person on
Earth, Mars, Venus, and Neptune.
Movie
“Laws of Motion”
Homework
“Gravity and the Planets” worksheet
Be ready for a quiz covering section 7.3
next time!