1. How does gravity affect falling objects?

2. Gravity and Free Fall Aristotle vs Galileo Aristotle believed that increased mass would equal increased acceleration, but Galileo proved that all objects accelerate to Earth at the same rate due to GRAVITY

3. Notice the distance is increasing because it is moving faster.
Falling Objects
The rate of falling increases by 9.8 m/s every second.(constant acceleration leads to an increase in velocity)
So, every second the object is falling it gains velocity.
Objects dropped from a higher position will hit at a faster speed.
The longer an object is falling the faster it is

4. W = m g The object will land with more force but not more speed!!!
Weight = the force of gravity
The weight of an object is, by definition, the strength of the force of gravity pulling the object downward.
force of gravity
W = m g
newtons kg
Another word for the force of gravity is the weight of the object on which gravity is acting.
{READ THE SLIDE}
So objects with more mass will be pulled with more force from gravity, therefore
the object weighs more.
The object will land with more force but not more speed!!!

5. How can we calculate the speed at which an object hits a surface?
Formula: Change in velocity: g x t
Velocity will be 0m/s at rest.
Change or Final Velocity= the speed at which it hits or stops
g= 9.8m/s/s ( this is the acceleration due to gravity
t= time it took the object to fall

6. Let’s practice a problem.
Alice drops a penny from the top of her apartment building. What is the penny’s velocity after it falls for 2 seconds.
Velocity = g x t
Velocity= 9.8m/s/s x 2 =
Velocity of the penny = 19.6m/s
If it takes the penny 10 seconds to hit the ground, what is its final velocity?
Velocity= g x t
Velocity = 9.8m/s/s x 10 s
Velocity= 98m/s/s Remember air friction is neglible!!

7. Free Fall and Acceleration due to Gravity
Free fall- when gravity is the only force acting on an object (free fall acceleration is directed toward the center of earth)
Only occurs in space and a vacuum
The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2. (This would be different on another planetary body)
Galileo found that all things fall at the same rate in the absence of air resistance, regardless of their mass

8. Free Fall Continued
A ball thrown horizontally will fall at the same rate as a ball dropped directly.
The horizontal motion is not affecting the rate of vertical acceleration!!!

9. More Free Fall
A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity.
When it passes the thrower again, it will be traveling at the same rate at which it was thrown.
Guess What?
The rate at which it slows on the upward vertical motion is also 9.8m/s/s!!

10. Air Resistance Happens!!!
So, what happens when there is significant air friction?
Air Resistance Happens!!!
It is the force that opposes motion of objects through the air. (pushes in the opposite direction of the motion)
Air resistance is dependent on size, shape, and speed of the object.

11. Air Resistance In air… In a vacuum A stone falls faster than a feather
Air resistance affects stone less(shape)
In a vacuum
A stone and a feather will fall at the same speed.

12. Larger Surface Area= more air friction or resistance to fall As speed increases air resistance increases (air molecules are packing up as the object moves faster and faster) Eventually the upward force of the air will equal or balance the downward force of gravity(Net force will equal 0) When this happens you have TERMINAL VELOCITY

13. Terminal Velocity: When gravity and air friction are balanced
Terminal Velocity: When gravity and air friction are balanced. Inertia continues to make the object fall, but it is no longer accelerating. It will fall at a constant speed!!

14. Terminal Velocity is not the same for all objects.
A person falling reaches a terminal velocity of around
54 m/s which means the person stops accelerating b/c:
Force of air resistance = gravitational force
With a parachute, terminal velocity is only 6.3 m/s
Allows a safe landing

15. What about Orbiting Objects?
They are in True FREE FALL!!!!
No other forces are acting on these objects.
Objects cannot be weightless anywhere in the universe because there is always some amount of gravity pulling on them.
Astronauts seem to float, but they are really falling around the planet.

16. Free Falling Orbits 2 motions combine to cause orbiting
Forward motion and a free fall
As objects move forward, they are also falling this combination makes the result a fall around the gravitational object such as Earth.
Ex. Moon orbiting Earth
Satellites orbiting Earth
Planets orbiting the Sun

17. Part 2 Projectile motion

18. Projectile Motion
An object thrown upward at an angle to the ground follows a curved path called a parabola.
combines vertical and horizontal motion
Orbiting objects- forward motion combines with free fall and object follows a curved path

19. Example. Playing catch with a softball
The trajectory has 3 parts.
free fall
the throw
the catch
What is the force acting on the ball, during each part of the trajectory?

20. Free Fall Review
Dropping something from a resting position (gains speed as it falls so it accelerates)
Gravity pulls objects down (air resistance can affect how fast) (no air resistance- in a vacuum)
When gravity is the only thing that affects falling object → FREE FALL
Acceleration due to gravity is 9.8 m/s2 on Earth

21. Free Fall equations V = g x t
A penny is at rest then dropped from the top of a 10 story building. What is the penny’s velocity after is has fallen for 2 seconds? What is its velocity at 4 seconds?
V= 9.8m/s/s x 2s V= 9.8m/s/s 4s
V=19.6 m/s V= 39.2s