Motion Chapter 9 Describing Motion an objects distance

Motion Chapter 9

Describing Motion – an objects distance from another object is changing. Reference Points – a place or object used for comparison to determine if something is in motion. i. e. a tree or building

Distance vs. Displacement Distance Displacement Total length of a path b/w two points. Length and direction of a straight line b/w starting and ending point. Total length = 7 Displacement = 5 NE 5 3 4 Vector – measurement with a size and direction

Speed is the distance an object travels per unit time speed = distance time Ex. 45 m/s SI unit for speed is m/s

Most speeds are not constant. Take a bike race for example. To find the speed of the total race for the bike we compute the Average Speed. Avg Speed = total distance total time Sample Problem: A cyclist goes 32 km in the first 2 hr and then goes 13 km for the next 1 hr Total distance = 32 km + 13 km = 45 km Total time = 2 hr + 1 hr = 3 hr Avg Speed = t 45 3 = 15 km/hr

Sample Problems Car trip: 100 km first 2 hr 150 km next 3 hr Car trip: 80 km/hr for first hr 40 km/hr next 2 hr Avg Speed = total distance total time First hr = 80 km Next 2 hr = 80 km = 100 + 150 2 + 3 = = = 250 5 50 km/hr 80 + 80 2 + 1 = 160 3 = 53 km/hr

Velocity A tornado is blowing at 100 mph. What else do the people in these homes need to know? Direction Velocity = speed + direction 100 mph NE

3 ways in which velocity changes Speed Direction Both speed and direction

Who works with velocity Air traffic controllers Pilots Weather people

Graphing Speed Shows motion of an object on a line graph plotting distance vs. time Slope = rise run Steeper the slope, the quicker the speed

Acceleration The rate at which velocity changes with time. Occurs in 3 ways: 1. increasing speed – ostrich standing still to running 2. decreasing speed – (deceleration or negative acceleration) stepping on the brakes 3. changing direction – softball changes direction when it is hit

A curved line on a distance vs. time graph tells you that the object is accelerating. SI unit for acceleration is meters per second or m/s²

Solving for Acceleration: An airplane starting at 0 m/s goes down a runway and 5 sec later takes off at 40 m/s. What is its acceleration? Acceleration (Acc) = Final velocity – initial velocity time = = = 40 m/s - 0 m/s 5 s 40 5 8 m/s² Go to pg 353 do problems 1 & 2 and pg 355 do prob. 4 & 5. 1. 2. 4. 5. 10 m/s² 3 m/s² 10 m/s²

Energy Work – when an object is caused to move a certain distance Energy – ability to do work or cause change

Kinetic Energy - Energy of a body due to it motion. K. E. = ½mv² m = mass, v = velocity Greater mass = Greater K. E. Less mass = Less K. E. Greater speed = Greater K. E. Less speed = Less K. E.

Potential Energy of a body based on its position, not in motion. The higher up something becomes the greater the gravitational potential energy. What is going to hurt more, falling off of a chair or falling off of a roof? Why? The roof, because there is a greater amount of potential energy.

Mechanical Energy – an objects combined kinetic energy and potential energy. M. E. = K. E. + P. E. Kinetic Energy→ 39 J Potential Energy 12 J M. E. = 39 J + 12 J = 51 J (J = joules)

Law of Conservation of Energy Where does the energy go from a spinning top? It is transferred into another type of energy. Law states that energy cannot be created or destroyed.