# Free Fall Centers - PowerPoint PPT Presentation

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Free Fall Centers. Let’s Reflect. Will Paper Fall Like a Stone ?. What happened?. Will Paper Fall Like a Stone?. Dropping the sheet of paper to the floor by itself will make it move from side to side and descend slowly because of the air resistance.

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Free Fall Centers

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## Free Fall Centers

Let’s Reflect

### Will Paper Fall Like a Stone?

• What happened?

### Will Paper Fall Like a Stone?

• Dropping the sheet of paper to the floor by itself will make it move from side to side and descend slowly because of the air resistance.

• The book is heavy enough to overcome the air friction and it drops in that short distance as if there were no resistance.

• Together, our intuition says that the paper should stay behind the book in falling to the floor, but they fall at the same rate because under the paper there is no air and thus no resistance. It is as if the paper fell in a vacuum.

### The Falling Pennies

• What happened?

### The Falling Pennies

• As both pennies were released at the same moment, the force of gravity started to work on the pennies at the same time.

• The downward component of the forces working on each of the pennies is therefore the same, and thus also the acceleration they obtain, resulting in reaching the floor in exactly the same time.

• This is why only one loud click (first click) is heard of the two pennies falling, regardless of the initial horizontal force imparted on one of them.

• In our case the air resistance was disregarded, because of the relatively short distance of fall.

### The Falling Washers

• What happened?

### The Falling Washers

• The falling weights are all subjected to gravity. The force of gravity imparts an accelerated motion to each of the weights.

• Because the force and mass of the weights are equal, the acceleration of each of the weights is the same.

• The difference is that the further the weight falls, the greater the velocity (v = at) of the weight when it hits the pie pan.

• When the weights are placed at regular intervals, the arrival is irregular, getting faster and faster, due to increased velocity (acceleration of gravity X time).

• The weights in the second demonstration also have equal increasing velocity, but because of the increased distance between weights, they arrive at even intervals.

### Water Bottle Drop

• What happened?

### Water Bottle Drop

• While you were holding the leaky bottle, gravity was pulling both the bottle and water toward Earth, but only the water was falling. You held the bottle against the pull of gravity.

• When you dropped the bottle, both the water and bottle were in free fall. The only force was the pull of gravity, which acted equally on the water and the bottle.

• If you poked a hole in the side of a bottle while free falling in an elevator, or while orbiting Earth, the water would remain in the bottle. The only force acting on the bottle and the water is gravity.

### Galileo

• What happened?

### Galileo

• Objects in general fall toward Earth, not away from it.

• Galileo Galilei showed that the mass of a falling body does not affect its rate of fall.

• All objects fall towards the Earth at the same rate, 9.8m/s/s (negating air resistance).

### Sky Diving Felix Baumgartner

• What happened?

### Sky Diving Felix Baumgartner

• After jumping from his platform at 120,000 feet, Baumgartner fell and accelerated to the speed of sound (343.2 meters per second or 768 miles per hour) because of the sparse atmosphere at the high altitudes where he released. The maximum speed he achieved is much higher than what it would be at lower levels where the atmosphere is thicker.

• As he descended and got closer to the Earth the thickening atmosphere actually slowed him up so he wouldn’t be falling nearly as fast. Once his parachute opened, it's not as if he will be going immediately from the speed of sound to the speed of a skydiver falling with an open parachute. He will have slowed down significantly by the time he reaches that altitude.

### Roller Coaster Physics

• What happened?

### Roller Coaster Physics

• Examples of Free Fall…

- skydiving

- roller coasters

- elevators

- Base jumping

### Galileo Goes to the Moon

• What happened?

### Galileo Goes to the Moon

• Because they were essentially in a vacuum, there was no air resistance and the feather fell at the same rate as the hammer, as Galileo had concluded hundreds of years before - all objects released together fall at the same rate regardless of mass.

### Free Falling and Weightlessness

• What happened?

### Free Falling and Weightlessness

• The astronauts experience weightlessness not because there is no gravity. Rather, weightlessness occurs because they and their spacecraft are free-falling in gravity. When two objects fall freely, one can float inside the other until they both reach the ground. The astronauts float inside the space shuttle just as water might float inside a falling cup -- even if that cup had holes in it.

• But what keeps the space shuttle from free-falling to Earth's surface and crashing into it? A spacecraft can maintain its free-fall for a very long period of time by traveling fast enough -- about 7.5 kilometers (4.7 miles) per second -- horizontally, so that even though it is constantly being pulled toward Earth's surface, its free-fall path is parallel to the planet's curvature.

• How might we simulate free fall on Earth?

### Why Doesn’t the Moon Fall Down?

• What happened?

### Why Doesn’t the Moon Fall Down?

• The Moon is falling towards Earth. However, it also has an orbital speed from the momentum gained during its formation that allows it to fall around Earth with a trajectory that follows the same curve as Earth's surface. Because these paths are parallel, the Moon perpetually falls around Earth without ever touching it.

• In general, the stronger the force of gravity, the more speed is needed to keep the planet falling around, instead of into, the object it is orbiting. Because the force of gravity weakens with distance, there is less gravity farther away from the Sun, so less speed is needed to keep an object in orbit.

### Terminal Velocity: Free Falling

• What happened?

### Terminal Velocity: Free Falling

• The filter that is less spread out falls faster.

• The greater the surface area of the falling object, the more air molecules the falling object strikes per second.

• An increase in the number of air molecules striking the surface of the falling object increases the upward force or drag on the object.

• With an increase in drag, the acceleration of the falling object decreases, as indicated by an increase in the time it takes the object to fall.

### Elevator

• Apply what you have learned to an elevator ride.

• How do you feel on an elevator when it goes upward? Downward? When it comes to a stop?

• If you were standing on a scale in an elevator, would your weight appear to increase, decrease or stay the same as the elevator rises?

• Would your weight appear to increase, decrease or stay the same as the elevator descends?

• Pretend that the elevator cable breaks and you are plummeting towards the earth, would your weight appear to increase, decrease or stay the same?