Air Resistance and Falling Objects
If we dropped objects in a vacuum, they’d accelerate downwards, without ever reaching a terminal velocity. They’d keep accelerating until they hit the ground. Behold: A ball and a feather, both dropped here on Earth, but in a vacuum!
What is terminal velocity?
When a body is first released, at time = 0 seconds, it has weight ( gravity x mass) but it has no downward velocity
At time t = 2 seconds, gravity has been accelerating it down
Now it has a vertical speed, and the same weight.
At time t = 10 seconds, it is moving so fast that the air friction, “drag”,
has as much force as the weight.
At this point it no longer picks up more speed.
We can explain it like this:
So what happens when a skydiver jumps out of a helicopter?
Watch how the numbers change as time goes by.
Penny drop: If you dropped a penny from a skyscraper, would gravity accelerate it to a deadly speed, before it hits terminal velocity?
The Empire State Building
Plans for zeppelin docking at the Empire State Building
Goodyear Zeppelin Columbia over Empire State Building after depositing copies of New York Evening Journal it had picked up from the Hearst Building in celebration of Journal’s 35th birthday.
Episode 4 – “Penny Drop”,October 17, 2003
2016 Massachusetts Science and Technology/Engineering Standards
HS-PS2-10(MA). Use free-body force diagrams, algebraic expressions, and Newton’s laws of motion to predict changes to velocity and acceleration for an object moving in one dimension in various situations.
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)
PS2.A Forces and motion. How can one predict an object’s continued motion, changes in motion, or stability?
Massachusetts Science and Technology/Engineering Curriculum Framework (2006)
Introductory Physics. Motion and Forces. Central Concept: Newton’s laws of motion and gravitation describe and predict the motion of most objects.
1.1 Compare and contrast vector quantities (e.g., displacement, velocity, acceleration force, linear momentum) and scalar quantities (e.g., distance, speed, energy, mass, work)
1.2 Distinguish between displacement, distance, velocity, speed, and acceleration. Solve problems involving displacement, distance, velocity, speed, and constant acceleration.
1.3 Create and interpret graphs of 1-dimensional motion, such as position vs. time, distance vs. time, speed vs. time, velocity vs. time, and acceleration vs. time where acceleration is constant.
Physical Setting/Physics Core Curriculum (New York)
Key Idea 5: Energy and matter interact through forces that result in changes in motion
5.1 Explain and predict different patterns of motion of objects (e.g., linear and uniform
circular motion, velocity and acceleration, momentum and inertia).
i. construct and interpret graphs of position, velocity, or acceleration versus time
ii. determine and interpret slopes and areas of motion graphs
iii. determine the acceleration due to gravity near the surface of Earth
5.1e An object in free fall accelerates due to the force of gravity. Friction and other
forces cause the actual motion of a falling object to deviate from its theoretical motion.