UNIT 5 FREE FALL

FREE FALL



FREE FALL

The moving of an object under the influence of the Earth’s gravity only, and no other forces, is referred as free fall.(Air resistance and friction are negligible).Free fall is motion with constant acceleration a=g , which referred as the free-fall acceleration or acceleration of gravity.
In this unit we assume that the initial velocity is zero.




JUMPING


THE VECTOR OF ACCELERATION DUE GRAVITY ( g )


 Click on the image


 Click on the schema

diagrama 1


 Click on the schema

diagrama 1


 Click on the schema

diagrama 1


Equations

The motion of an object in free fall can be described by kinematic equations.



 Click on the image


             The kinematic equations are:


 Click on the image


Apple's free fall


 Click on each tab

 Click on the schema

diagrama 1

 Click on the schema

diagrama 1

 Click on the schema

diagrama 1


Total time ttot and final (impact) velocity υof the motion


Imagen

Graphs

Τhe graphs of position-time  and velocity -time  are the following.


Imagen
Imagen

ELEPHANT AND FLY

From the equations above we can see that , if air resistance is negligible ,then objects with diferent masses fall with the same constant acceleration , which is independent of their mass.

For example, an elephant and a fly...


 Click on the schema

diagrama 1


A FEATHER AND A HAMMER

Ιf air resistance is negligible then a feather and a hammer fall with the same constant acceleration . Astronaut, David R. Scott demonstrated this ,1971 on the Moon, where there is no atmosphere and the gravity's acceleration is 1.67 m/s2
The following video is from Apollo 15 Video Library ( https://history.nasa.gov )
APOLO 15 LIBRARY


FEATHER AND HAMMER

CHOOSE OPTION



 Click on the correct option

1. The unit of g (acceleration due gravity) is equal to

Imagen 1

 Click on the correct option

2. The force of gravity on an object on the surface of earth, is called

Imagen 1

 Click on the correct option

3. The unit of w (weight), is equal to:

Imagen 1

 Click on the correct option

4. The reason that pulls falling objects toward Earth is a force, called

Imagen 1

 Click on the correct option


 Click on the correct option

6. The acceleration of an object ,falling freely near the surface of the earth (Assume there is no air resistance )

Imagen 1

 Click on the correct option

7. A feather and a hammer dropped from rest , from the same height at the same time ,would land at the same time when dropped

Imagen 1

 Click on the correct option

8. A 10Kg iron ball is dropped from rest , from the roof of a building 45 meters tall. What is the time of fall? (Assume there is no air resistance and g=10m/s2 )

Imagen 1

 Click on the correct option

9. Suppose that, three balls of different materials are dropped from rest ,at the same time from the same height, the ball which hit the ground first is (Assume there is no air resistance and g=10m/s2.)

Imagen 1

 Click on the correct option

10. A stone is dropped from a bridge 80 meters tall. The velocity of the stone just before hits the water is (Assume there is no air resistance and g=10m/s2 )

Imagen 1

FILL THE GAP



 Answer each question

1. An object falling freely, toward the surface of the earth, has a velocity, that is ____

2. Suppose an object is falling freely. During the 2nd second the object falls ____ distance than in the second before

3. A physics Book rests on a 1,8 m high bookshelf. It takes ____ s for the book to fall to the floor. (Assume there is no air resistance and g=10m/s2 )

4. An apple is dropped from a tree ____ m tall and It takes 0,7s s for the apple to reach the ground. (Assume there is no air resistance and g=10m/s2 )

5. A stone falls from a gorge. Its velocity after 6 seconds of falling is ____ m/s (Assume there is no air resistance and g=10m/s2 )

6. A watermelon falls from a high building and hits the ground 5 seconds later, the distance that it fell is ____ m (Assume there is no air resistance and g=10m/s2 )

7. A ball falling freely near the surface of the earth has an acceleration that is ____

8. Obelix drops a menir , from a bridge 20 meters tall , from rest, downwards to a roman soldier 2m high . The strike velocity is ____ m/s approximately

9. An apple falls from the the Petronas Towers, in Kuala Lumpur, Malaysia (450 meters height ) and takes ____ seconds approximately to reach the ground.

TRUE OR FALSE



 Classify in true or false

1. A rock and a feather are dropped at the same time, from the same height, in a vacuum.The rock will reach the ground earlier.

2. Velocity and acceleration are both vectors

3. The direction of the acceleration due gravity is perpendicular to the radius of the earth

4. The symbol g stands for the weight of an object

5. Free fall occurs only in a vacuum

6. The value of g varies at different places on the earth

7. Free fall is a motion with constant acceleration

8. Gravity is not a force, it is an acceleration

9. In free fall motion we assume that air resistance is negligible

10. The value of g increases with increasing altitude above the Earth’s surface


Watch the following video

g=10m/s2  


FALL


 Match each concept with its definition


Please watch the following interactive video and choose the right answer.


FALL IN PARIS


Imagen