Unit 1 - Kinematics - Free Fall

An object in free-fall is under the influence of ___________.

gravity

instantaneous speed formula

instantaneous speed = acceleration x elapsed time (v = gt) [v = (10 m/s2)t]

What happens to the velocity as the object moves upward?

it decreases

What is happening to the speed as it moves downward?

it increases

Why did both reach the ground simultaneously unlike the earlier case?

they are both in free fall, meaning only gravity is acting on the objects

General equations (starting from rest)

v = at and d = 1/2at2

Freefall equations (starting from rest)

v = gt and d = 1/2gt2

"New" formulas

y = ½ (vi + vf)t. vf = vi + gt. y = vit + ½ gt2. vf2 = vi2 + 2gy. The positive y-direction has been chosen to be upwards. If it is chosen to be downwards, the sign of g would need to be changed.

Why do we use a negative for gravity (-9.8 m/s2)?

-9.8 m/s2 for gravity. It is negative because our reference point will be positive direction (+) is "up" and negative direction (-) is "down". Because gravity is pulling objects "down"

What is the speed at the maximum height?

0 m/s

A tennis ball is thrown vertically upward with an initial velocity of +8.0 m/s. What is the ball's speed when it returns to its starting point? How long will the ball take to return to the starting point?

1.6 s

A flowerpot falls from a windowsill 25.0 m above the sidewalk. How fast is it moving when it hits the ground? How much time does a passerby have to get out of the way?

22.2 m/s downward, 2.2 seconds

Acceleration is independent of

Mass

What do we need to get rid of to be able to see the true nature of gravity?

Air

Free fall definition

An object moving under the influence of gravity only is said to be in free fall. The instantaneous speed increases by 10 m/s each second.

Any change in velocity is....?

Any change in velocity is an acceleration.

A boy on a bridge throws a stone vertically downward with an initial speed of 14.7 m/s toward the river below. If the stone hits the water 2.0 seconds later, what is the height of the bridge above the water?

Bridge is 49.4 m high

Which of the following is the reason that the distances are increasing?

Gravity is accelerating it.

A ball is thrown straight up in the air: At the peak of its ascent, what is it doing?

Instantaneously at rest

An object moving in a positive direction in free fall means?

It's moving up

Why does the ball start to decelerate?

The force of gravity is pulling it downwards towards the surface of the earth.

What letter represents acceleration in free fall?

The letter g. The acceleration due to gravity: g = 10 m/s2. (Also used is 9.8 m/s2 for labs). The speed changes by 10 m/s each second on the way up and on the way down.

Free fall (more definitions)

The motion of a body when only the force due to gravity is acting on the body. Acceleration due to gravity. ag (generically) or g (on Earth's surface). Free fall acceleration is the same for all objects. g = -9.81 m/s2. all points in the object's motion.

When the feathers and bowling bowl were dropped at the exact moment in a near perfect vacuum, what happened?

They fell at the same rate and landed at the same time

In perfect conditions, which will hit the ground first?

They will hit the ground at the same time.

g represents the ________________.

acceleration of gravity