& AIR RESISTANCE The physics of falling GRAVITY & AIR RESISTANCE The physics of falling

The Force of Gravity Gravity is the force that pulls all objects down to the earth. Rain falls from the sky down to earth… If you drop a book, it falls to the ground… If you trip, you’ll fall down…

Universal Gravitation Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book) The force of gravity is much STRONGER for LARGER objects (more mass).

Universal Gravitation Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction... So, no matter where you are on earth, all things fall to the ground due to gravity…

What is “free fall”? When gravity is the ONLY force acting on an object, it is in free fall. In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate.

Acceleration due to Gravity Calculate the acceleration of an object in free fall. A = Final speed – initial speed time A = 50 m/s – 0 m/s 5 s Acceleration = 10 m/s2

Objects in Free Fall Do all objects fall at the same rate? If we dropped a bowling ball and a tennis ball from the same height, which would land first? Let’s try it!

Question: How does mass affect the speed of a falling object? Mass and Gravity Oct. 24, 2008 Question: How does mass affect the speed of a falling object? Hypothesis: (What do you think will happen AND WHY?) Observations & Data Collection: Repeat each trial twice and record your observations. Ping pong ball vs. Wooden ball: Wooden ball vs. Metal ball: Ping pong ball vs. Metal ball: Conclusion: (One sentence)

Objects in Free Fall Do all objects fall at the same rate? ALL objects in free fall travel at the same rate, regardless of mass! In free fall, heavy objects and light objects fall at the same rate!

So, which will land first? WHY does the penny land first? Remember the force that opposes motion (slows things down)? FRICTION! Falling objects experience friction with the air called AIR RESISTANCE that slows them down.

Air Resistance The larger the object (more surface area), the more air resistance. That’s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall.

Air Resistance Draw a diagram showing the forces… Gravity Draw a diagram showing the forces… Downward force of gravity is same on both. Upward force of air resistance is greater on the feather. The net force (down) is greater on the penny. Net Force on Penny Net Force on Feather

Without air resistance, all objects would fall at the same rate… Galileo Drops the Ball Hammer and Feather Drop on the Moon

That’s why astronauts weigh less on the moon! Gravity on the moon? The force of gravity is much weaker on the moon because… It is much farther away from earth. The moon is much smaller than earth. That’s why astronauts weigh less on the moon!

Gravity Review Gravity is the force that pulls all objects down to the earth. When gravity is the ONLY force acting, ALL objects accelerate at a rate of 10 m/s2. Mass doesn’t matter – in free fall, heavy objects and light objects fall at the same rate!

Air Resistance Review Some objects take longer to fall – they are slowed down by FRICTION with the air called AIR RESISTANCE. The larger the surface area, the greater the force of air resistance pushing up. Without air resistance, all objects would fall at the same rate…

Draw a free body diagram of the sky diver and label ALL the forces. Gravity = 1000 N Air Resistance = 800 N What is the net force? Air Resistance = 800 N Net Force = 200 N Gravity = 1000 N