Section 3 Average Speed: Following Distance and Models of Motion WDYS? (p34) 1. 2. 3. WDYT? (p34) 1. 2. 1-3 Investigate use strobe photos to observe constant motion at different speeds
1-3 Investigate (p34-36)
Describing Motion and Speed Using Strobe Photos (p37) Speed the distance traveled per unit of time (d/t) Speed affects your following distance, braking distance, and total stopping distance Constant Speed speed that does NOT change over time, it stays the same EXAMPLE Constant SLOW Speed Constant FAST Speed The distance between the car images are evenly spaced out close together farther apart
Describing Motion and Speed Using a Distance-Time Graph (p41-43) A second way to represent motion is with GRAPHS, where time is on the x-axis and distance on the y-axis Anytime an object moves at a CONSTANT speed, the distance-time graph is a STRAIGHT line
Graphs: What s happening?
Speed and the Slope of Distance-Time Graph You compare speeds by looking at slopes Slopes = Rise ( y-axis) Run ( x-axis) Velocity = ( d) ( t) The steeper the slope, the faster the speed The flatter the slope, the slower the speed
Describing Motion and Speed Using an Equation (p37-41) Average Speed total distance traveled divided by the time it took to travel that distance The Greek letter delta means a change in and is calculated by FINAL INITIAL Instantaneous Speed the speed at any given moment, it is read on the speedometer Velocity speed WITH direction
Equations speed = distance / time v = d / t t = d / v d = v * t Units for speed (v) : m/s km/h time (t) : s h distance (d) : m km It is very important to pay close attention to the units in your math work and answers!!!
Kilometers and Miles (p43) United States = miles per hour (mph) Everywhere else = kilometers per hour (km/h) 1 mile = 1.61 km
Speed and the Doppler (p44) Part of safe driving is obeying the speed limit: 1. Read the speedometer 2. Use posted mile marker and measure the time 3. Sound of engine and tires Doppler Effect the change in pitch 1. Ambulance sirens 2. Police radar guns
Reaction Distance (p46) Reaction Distance the distance that your car travels UNTIL you respond ***While you decide what to do, you need to remember that the car is still traveling over the ground*** A longer (slower) reaction time increases the distance you travel therefore increases the chances of an accident
Derived Units The International System of Units (SI) a system based on the multiples of TEN (10) used by all scientists around the world a) Length meter b) Mass (kilo)gram c) Volume Liter d) Time second e) Temperature Kelvin
Derived Units Cross-Dimensional Analysis (Conversion) Measurements consist of two parts the number and the unit Examples 10 apples 12 oranges 20m 4.3kg You cannot compare apples to oranges only apples to apples and oranges to oranges Therefore it is NOT possible to combine two numbers UNLESS they have the SAME units Derived Units obtained by combining 2 or more base units together
1-3 Checking Up Questions (p46) 1. The average speed of a vehicle is different from instantaneous speed by 2. Speed and velocity of an object different by 3. If the distance-time graph shows a straight & inclined line, the line represents 4. Reaction time affects reaction distance by
1-3 WDYTN? (p48) What is a safe following distance between your automobile and the vehicle in front of you? 1) 2) How do you decide what a safe following distance is? 1) 2)
1-3 PEQ (p48) 1. The speed of a vehicle going 40mph means 2. I would measure the speed of the car by measuring the it takes for the vehicle to travel a specific. I would use a to measure time while a to measure distance. The equation for speed is. 3. A strobe photo shows An equation calculates A graph shows 4. Reaction distance depends on your reaction time and your speed because
1-3 PTG(p49-51) 1. a) b) 2. a) b) 3. 4. a) b) 5. 6. a) b) c) d) 7. a) b) c) 8. a) b) 9. a) b) 10. a) b) c) d) e) 11.
1-3 PCC (p51) 12. Apply what you learned in this section to write a convincing argument that describes why tailgating is dangerous. Include the factors you would use to decide how following too closely counts as tailgating.