Friday, Jan. 29 th Agenda Collect Homework: “Isaac Newton” WS Finish section 7.3: –free fall, weight, terminal velocity, Newton’s 3 rd 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/s 2.

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 3 rd 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 3 rd Law  The upward push on the rocket equals the downward push on the exhaust gases.

Newton’s 3 rd 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!