# Speed & Velocity Speed & Velocity Chapter 2.1 Todays Agenda 01/23: PPT 2.1 Distance vs. Displacement Lab 2.1 Determining Velocity & Acceleration EOC Chapter 2.1 Quiz 2.1 Open 01/20 - 01/25 Explain

distance vs. displacement 3,4,5 right triangle Motion is Relative Everything moves! That is, in respect to other things. A book on a table may seem to be stationary, but in reality it is moving about 1040 mi/hr relative to the center of the Earth, 700 mi/hr relative to the sun and about 30,000 mi/hr relative to the

center of the Milky Way! What is the difference between speed and velocity? scalar One-component (magnitude) e.g. speed m/s vector

Two-component (magnitude & direction) e.g. velocity m/s E Speed Speed = Speed =

dx time = unit of dx unit of time dx time Units (Miles/hour; Km/sec = Change

cm/day; L-yr/century) Units of Conversion 5280 feet = 1 mile 1 meter = 3.28 feet 1 inch = 2.54 cm 1000 meters = 1 km 1 km = .62 mile Calculating Speed

If you ride a bike a dx of 5 m in 1 sec, what is your speed? What is your speed in miles/hr? What is your speed after traveling 10 m in 2 sec? For 100 m in 20 sec? Instantaneous Speed Instantaneous Speed The speed at any instance in

time (the speed the speedometer reads at any moment) Average Speed Average Speed Speed computed for the entire duration of a trip.

Average speed = Total distance Total Time interval , s = d/t Calculating Speed If the odometer reads 0 at the beginning of a trip and 35 km a half hour later, what is the average speed?

s= Total dx = 35 km = 70 km Time hour hour Holiday Trip What is your average speed

for the entire trip? Titusville New Orleans (13 hours) 657 mi New Orleans Memphis

(8 hours) Memphis Atlanta (11 hours) Atlanta Titusville (8 hours) 490 mi

480 mi 921 mi If a cheetah can maintain a constant speed of 25 m/s, it will cover 25 meters every second. At this rate, how far will it travel in 10 seconds? in 1 minute? dx = speed x time

Graphing Motion When graphing distance vs. time, always make distance the y-axis and time the x-axis Reading a Motion Graph

Reading a Motion Graph Slope of dx vs. t graph = speed s = dx/t (-) speed means object is coming towards Reading a Motion Graph How fast was car going from

A B? B C? C D? Graphing Motion Distance (meters) 3 meters

3 seconds Time (seconds) The slope of a line on a distance-time graph is speed Graphing Motion If the slope of a dx-time graph is constant (i.e. straight), then the speed is constant.

Dx slope = 2 Time Graphing Motion If the slope is zero, the speed is zero. Dx

slope = 0 Time Graphing Motion Negative speed (means object is coming at you) Dx

slope = negative Time Graphing Motion No negative velocity! Dx

slope = negative Time Velocity Remember, velocity is speed + direction (vector) A car is traveling 60 m/hr is its speed. A car traveling 60 m/hr north is its velocity! Constant Velocity

Constant velocity = constant speed AND constant direction If either the speed or direction change, the velocity changes. Constant speed = Constant velocity 3 Components effect velocity in a car: acceleration pedal; brake; steering wheel Velocity If an airplane travels 500 km due north in 1 hour,

what is its velocity? If it travels 250 km due north in hour what is its velocity? Velocity Remember, velocity is a VECTOR meaning it has both magnitude and direction. It is represented schematically as an arrow. The arrow tip shows direction and the length is equivalent to the magnitude.

10 m/s N 3 m/s E 6 m/s NE Combining Velocities Vectors can be added 12 km/hr E

and subtracted! 12 km/hr E 5 km/hr E 5 km/hr W Vtotal = 17 km/hr E Vtotal = 7 km/hr E

Velocity If an airplane is traveling due East at a constant velocity of 200 km/hr and theres a strong Easterly wind blowing at 15 km/hr, what is the airplanes resultant velocity? Combining Velocities Vectors can be added 120 km/hr E

15 km/hr E VR = 120 + 15 = 135 km/hr E The total velocity is called the Resultant velocity Velocity If an airplane is traveling due north at a constant velocity of 12 km/hr and it faces an easterly crosswind of 5 km/hr, what is its resultant

velocity? Combining Velocities Vectors can be added North 5 km/hr E Use Pythagorean Theorem to calculate

Resultant Velocity a2 + b2 = c2 122 + 52 = 169 = 132 12 km/hr N Resultant velocity is 13 km/hr NE