Chapter 4 Linear Motion Pages 46- 60

4.1 Motion Is Relative Relative motion: depends on the point of view, or frame of reference. “with respect to…” An object is moving if its position, relative to a fixed point, is changing. Motion is relative Click Mythbusters to watch a video!!

4.2 Speed Instantaneous Speed is the speed (observed) at any instant. The instant you look at your speedometer, you’re observing an instantaneous speed. Average Speed is the total distance covered divided by the time traveled. - Does not indicate variations in the speed over the duration of the trip. Speed is how fast an object is moving. Speed is calculated by dividing distance by time. Equation Triangle Any combination of units for distance and time are useful for speed Ex: Kilometers per hour (km/h) Ex: Centimeter per day (cm/d) The slash / is read “per” **Primarily use meters/second** d s t

4.3 Velocity Velocity is speed in a given direction. (Vector Quantity) Constant Velocity: means constant speed and constant direction. -Constant direction is a straight line- the object’s path doesn’t curve. Changing Velocity: if either speed or direction (or both) is changing, velocity is changing. - A car, driving at a constant speed in a circular path (Indy 500), is an example of changing velocity because the direction is constantly changing. Velocity is speed in a given direction. (Vector Quantity) Speed is a description of how fast an object moves; Velocity is how fast and in what direction it moves. 150 km/h North East 2.0 ft/day west 5.0 m/h South

4.4 Acceleration We can change the state of motion of an object by changing its: Speed, Direction of motion, or Both Acceleration is the rate at which the velocity of a moving object is changing. Acceleration is calculated by diving the change in velocity by the time interval . Calculating Acceleration a= acceleration Vf= final velocity (end) Vi= initial velocity (beginning) T= time frame

Acceleration Key idea that defines acceleration is CHANGE!! Press on the gas pedal (accelerator) , experience a change Slam on the breaks (deceleration), experience a change

Acceleration- the rate of change in velocity Change in Direction Acceleration also applies to a change in direction. You feel this when you go around a curve, and your body tends to move toward the outside curve. State of motion is changing; you are changing. CLICK HERE FOR A VIDEO! #acceleration Change in Speed When direction is not changing, acceleration may be expressed as the rate at which speed changes.

4.5 Free Fall: How Fast Does an object accelerate when it falls? Yes! In real life, air resistance affects the acceleration of a falling object. However, an object is in free fall as long as gravitation force is the only influence effecting its motion. The time passed as an object is falling is known as elapsed time.

Free Fall The acceleration of an object in free fall is about 10 meters per second squared (because it is falling towards Earth, downward, you’ll often see it considered “negative” 10 m/s/s.) For free fall, we use the letter g in reference to the force of gravity. To calculate the instantaneous speed of a falling object we use the equation: v = gt - v= speed/velocity (down) - g= acceleration due to gravity (10 m/s/s) - t= time elapsed

Free Fall Speed On Other Planets A MUST WATCH VIDEO ABOUT THE WORLD RECORD BREAKING FREE-FALL JUMP (SKYDIVE!) CLICK HERE- BUT ONLY IF YOU PROMISE TO WATCH THE WHOLE VIDEO!!!!

Rising (and Falling) of Objects Consider an object being thrown straight up… During the upward part of the objects motion, the object slows from its initial velocity to zero velocity. The slowing occurs due to gravities influence… gravity wants to take over the object but can’t, yet. As the highest point (peak) the object has slowed down so much, that it stops completely. We say that it’s instantaneous speed is zero. One stopped, gravity takes over the object and it begins falling- at a rate of 10 m/s/s (force of gravity).

Notice how the ball rises and falls in the same position, regardless of it going UP or DOWN. *This is DUE to GRAVITY!* Not only are the positions the same, the time it takes to accelerate is the same also!!! Velocity is also changing: Velocity is positive on its way up Velocity is negative on its way down Velocity is ZERO at the peak.

LET THE MYTHBUSTERS SOLVE THIS!!! IS IT TRUE THAT… - If you drop a penny from the top of _______ and it hits someone, it will kill them?! LET THE MYTHBUSTERS SOLVE THIS!!! CLICK ON THE PENNY!

4.6 Free Fall: How Far Speed and Distance are NOT the same thing- therefore how fast something is moving does not determine how far it has traveled. For each second in free fall, an object falls a greater distance that it did the previous second. Mathematical expression used to calculate this is: 1 2 𝑔 𝑡 2 Half- indicates we’re calculating the AVERAGE distance G- the force due to gravity T- the time ellapsed

4.7 We Will Do All Graphing Together!! Skip Book Notes For This Section

4.8 Air Resistance and Falling Objects Air resistance is responsible for differing accelerations among different objects. Air resistance noticeably slows the motion of things with LARGE surface areas (like feather) Air resistance is less noticeably affects the motion of more compact objects (like baseball) The ONLY place, for which air resistance does not exist, is within a Vacuum. Click HERE to watch a video about falling objects!

HANG TIME! PG 60 Hang time is the estimated amount of time a jumper is airborne (feet off the ground) Hang time is calculated: 𝑡= 2𝑑 𝑔 We can calculate YOUR hang time as long as we can measure the distance (height) for which you jumped! If you click on MJ- a magical compilation video of his greatest hanging moments will open!