11-KE and Acceleration due to Gravity

KE and Acceleration due to Gravity

We are going to learn why a belly flop from high in the air is a bad idea.

Speed & Velocity

Speed is a rate of distance over time. (s= d/t; unit- m/s or mph)

Velocity is speed in a given direction (the cheetah ran 15 m/s westward)

Acceleration is the rate in change of velocity.

Multiple Choice

The rate in change in velocity is called

• speed

• velocity

• acceleration

If an object is falling from the sky towards Earth's surface it is in 'free fall'

• Free fall is the motion of an object falling with constant acceleration

• g force- 9.8 m/s²

Multiple Choice

The motion of an object falling with constant acceleration is called

• gravity

• free fall

• force

Multiple Choice

ALL objects in free fall are attracted to earth with an acceleration of

• 9.8 m/s²

• 1.0 m/s²

• it depends on how much mass the object has.

Connection to KE

• When an object is released, it's velocity increases as it falls

• The increase in velocity, INCREASES the kinetic energy

• the higher up the object is, the MORE kinetic energy is released

• The object's mass and the drop height will affect it's velocity.

• ...but no matter the object, the object will accelerate the same (9.8 m/s²)

Case Study: Elephant and the Mouse

Who has the greater velocity?

Who has the greater acceleration?

Poll

Who has the greater velocity?

• the mouse

• the elephant

• they have the same velocity

Poll

Who has the greater acceleration?

• the mouse

• the elephant

• they both have the same acceleration

Pretend the elephant was the big rock and the mouse is the little rock.

• The elephant/big rock has greater velocity.

• It takes more force for the rock to maintain its acceleration to the ground.

So..while velocity may change the rate at which the change happens stays the same.

• Both the elephant and the mouse have the same acceleration.

Multiple Choice

If a mouse and an elephant fell from the same point, which would have the greater velocity?

• the elephant

• the mouse

• they would have the same velocity

Multiple Choice

If a mouse and an elephant fell from the same point, who would have the greater acceleration?

• the mouse

• the elephant

• they would both have the same acceleration.

What if there were two elephants but one fell from a 15 meter cliff and the other fell from a 40 meter cliff?

Which elephant would have the greater KE?

Poll

Two elephants...the first elephant falls from 15 m. The other falls from 40 m. Which elephant has the greater KE?

• the elephant that fell from 15 m

• the elephant that fell from 40 m

• they will have the same KE no matter what point they fell from.

The faster an object moves, the more KE it has.

As objects fall toward Earth it speeds up! The higher up the object is, then the faster it'll go to reach the ground. Remember...it is accelerating at 9.8 m/s², but the speed is increasing every second.

Multiple Choice

Case Study: Two Elephants

Which elephant will have the greater KE-- Elephant 1 from 15 m or Elephant 2 from 50 m?

• Elephant 1 will have more KE

• Elephant 2 will have more KE

• Both elephants will have the same amount of KE

Open Ended

The goal of our lesson today was to be able to explain how acceleration due to gravity affects kinetic energy.

Use what you've learned to tell us why doing a belly flop at this height is a bad idea.