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 WeightFree fall: the motion of a body when only

the force of gravity is acting on itBecause 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 MassMass: 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 VelocityTerminal 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 3rd LawNewton’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!