2-3 Falling Objects Gravity - the force of attraction between all matter.

Gravity – one of the FOUR FUNDAMENTAL FORCES in nature.

If there is NO AIR RESISTANCE, ALL objects, regardless of mass and size, will fall at the

same constant acceleration. – called FREE FALL

The Acceleration due to Gravity on earth is: a = g = -9.81 m/s/s

a = g = -10 m/s2

Hammer vs Feather

Galileo's Falling Objects off Leaning Tower of PisaGalileo's Inclined Plane

1. Why did the hammer and the falcon feather hit the ground at the same time on the Moon?

2. What would you predict if you dropped a hammer and a falcon feather on Earth? Would they hit the ground at the same time or at different times? Explain your reasoning.

3. If you couldn't go to the Moon, how could you create a situation on Earth to do this experiment?

Freely Falling Objects

Displacement vs time graph

Negative acceleration -10 m/s2

Velocity vs time graph

∆y = vyi∆t + ½ g( ∆t )2

Equations: Distance traveled (∆y) by an object after a given amount of time (∆t)

Where initial velocity = 0 m/s

Then, ∆y = ½ g( ∆t )2

Throwing up a ball:Velocity and Distance

Q: A ball is thrown straight upward and then returns to the Earth. Does the acceleration change during this motion?A: No

What is the acceleration?

-9.81 m/s2

-10/ms2 going up and coming down – g is a force pulling down towards the center of earth

What goes up must come down

Throwing Up a Ball: Velocity VS. Time graph

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

10Accel.

0(m/s2 )

-10 10Vel.

0(m/s)

-10

10

Disp.

(m)

0 Time (s)

IMPORTANT FORMULAS: See Ch 2 Outline for all formulas and don’t forget how we derived

formulas for time – total time that an object is in air … up and down … and just time an object is in air dropped from a set height.

∆y = vyi∆t + ½ g( ∆t )2

vyf = g ( ∆t )

y = yi + vi ∆t + ½ g( ∆t )2 ( if yi ≠ 0 )

vyf2 = 2 g( ∆y )