Motion in One Dimension Freefalling

What we know… Change in position is represented by ∆x = xf - xi How can we find acceleration on a velocity vs. time graph? Slope on a velocity vs. time graph is acceleration What is acceleration? A change in velocity (or direction) What happens when an object’s velocity & acceleration are in the same direction? Opposite direction? Same: the object gets faster Opposite: the object slows down

What we want to know… How does gravity affect an objects motion? How does an object in free fall compare to an object with constant acceleration? Does mass of an object affect it in free fall?

Free Fall Objects fall because gravity accelerates them towards the ground. Acceleration due to gravity on Earth is about 9.81 m/s². We use “g” to represent acceleration due to gravity.

Mass Does the mass of an object affect how fast it falls? In a vacuum (no air resistance) objects released at the same time will fall at the same rate regardless of mass (hit the ground at the same time from the same height.)

Free Fall Equations In free fall, the acceleration of an object is caused by gravity. a = g = 9.81 m/s²

Acceleration due to Gravity Unless acted upon, the rise and fall portions of vertical motion are symmetrical. Is the same at all points in an objects motion. Velocity’s direction? Acceleration’s direction? Moving up: velocity decreasing acceleration = -9.81 m/s² At top: velocity = zero Moving down: velocity increasing

Hang Time Hang time is the amount of time a jumper can stay in the air. The higher you jump, the more “hang time” you have.

Reaction Time Your brain takes time to interpret data (what you see, hear, etc.), decide on an action, and convey that action to your muscles. This is known as reaction time. Calculating reaction time: 1 person drops ruler 1 person catches it How far did it fall? How fast was the ruler right after you let go? What direction was everything going?

Demo A box of stuffed animals falls out of a plane flying perfectly parallel to the ground. If the plane was .62 miles above the ground, how long did it take for the box to hit the ground?

David is skydiving. If he jumps from a plane that was flying perfectly horizontal, how far will David fall after 9 s? What is his velocity at this point?

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