Today I will: Define free fall Define gravity Determine the instantaneous position and velocity of an object (how far and how fast)

Free Fall Free fall – an object that is only acted upon by gravity (air resistance is to small to account for it) Free fall is for objects moving down and UP

What is gravity? Gravity is a force that causes an acceleration (a change in velocity over time)

Falling Objects Near the surface of the Earth, all objects experience approximately the same acceleration due to gravity. **This is one of the most common examples of motion with constant acceleration.

Falling Objects In the absence of air resistance, all objects fall with the same acceleration --can be hard to tell by testing in an environment where there is air resistance.

Figure 2-20 A rock and a feather are dropped simultaneously (a) in air, (b) in a vacuum.

Ball and a feather Hammer and a feather

The acceleration due to gravity at the Earth’s surface is approximately 9.80 m/s2. (Note: it acts downward so it is negative)

Complete this statement: What goes up must….

Why?

What happens to objects as they move up?

How fast The instantaneous velocity of an object at any moment while in flight 𝒗 𝒇 = 𝒗 𝒊 + at Start with 3rd, 6th and 8th NOTE: The velocity we are finding is the instantaneous velocity which means it’s the velocity at that instant in time; it takes a full second to get to change your speed by 10 m/s

Today I will: Determine how fast and how far an object is falling at any second in time

How far The distance an object travels while in free fall NOTE: The average velocity can not be used to find distance….its only the velocity at that second in time (we can not just plug into d = vt!)

To find how far: Δd = vit + ½ agt2 Special Note: Remember Δd = df - di Special Note: For many problems we are starting from rest so our initial velocity (vi) is equal to zero; look for information in the problem

CDP Make sure you use -10 𝑚 𝑠 2 at all times! Note: Whatever 𝑣 𝑖 is to start; that is the 𝑣 𝑖 for the object the entire time in flight

Today I will: Explain the motion of an object in free fall in terms of time, velocity, distance and acceleration Review the 4 basic kinematic equations Solve motion problems for v, d and t

Kinematic Equations 𝒗 𝒇 = 𝒗 𝒊 + at ∆𝒅= 𝒗 𝒊 t + 𝟏 𝟐 a 𝒕 𝟐 Equation 1: Remember Δd = df - di Equation 3: Equation 4: **Used rarely

Looking at the equations in more detail… vf vi df di a t Equation 1 Equation 2 Equation 3

Oct 24, 2012 Today I will: Apply the concepts of free fall motion to solving motion problems for v, d and t using the appropriate kinematic equation

Example Free Fall Problems

PE 9-14