MECHANICS DESCRIBING MOVEMENT Instantaneous speed & velocity Graphs of Motion Equations of Motion
QUICK REVISION DISTANCE DISPLACEMENT VECTORS SCALARS SPEED VELOCITY ACCELERATION TICKER TIMERS
THE DIFFERENCE BETWEEN: AVERAGE AND INSTANTANEOUS
INSTANTANEOUS SPEED Equation? Vector / Scalar? Unit?
INSTANTANEOUS SPEED Definition: The speed of an object at a specific moment in time. The distance divided by a infinitesimal time interval. The magnitude The magnitude of the instantaneous of the instantaneous velocity. velocity. Speedometer Speed trap
INSTANTANEOUS VELOCITY Equation? Vector / Scalar? Unit?
INSTANTANEOUS VELOCITY Definition: The velocity of an object at a specific moment in time. The displacement divided by by an an infinitesimal time interval. interval. Magnitude of instantaneous speed and velocity are the same. Direction is = to that of a tangent to the path that the object is following.
GRAPHS OF MOTION Graphs used to describe the movement of an object. Plot points: X not Independent variable x axis Dependant variable Y-axis
GRAPHS OF MOTION 3 TYPES Position-time graph Velocity-time graph Acceleration-time graph
REPRESENTING CONSTANT VELOCITY Time (s) Total displacement from start (m) 0 0 1 10 2 20 3 30 4 40 5 50 6 60 7 70
REPRESENTING CONSTANT VELOCITY Choose any 2 co-ordinates from your velocity- time graph: ( ; ) ( ; ) Use these to calculate the gradient of your straight line.
REPRESENTING CONSTANT VELOCITY Using your velocity time graph, calculate the area of the shape made by the graph and the x-axis.
REPRESENTING POSITIVE ACCELERATION (1) on a position time graph You re speeding up INSTANTANEOUS velocity? AVERAGE velocity?
The gradient of an intersecting line joining 2 points in a parabolic x-t graph gives the average velocity of the object between time t1 and t2. The gradient of a tangent to a parabolic x-t graph gives the instantaneous velocity of the object at time t1
REPRESENTING POSITIVE ACCELERATION (2) on a velocity time graph You re speeding up
REPRESENTING POSITIVE ACCELERATION (3) on an acceleration time graph You re speeding up
REPRESENTING NEGATIVE ACCELERATION (1) on a position time graph You re slowing down.
REPRESENTING NEGATIVE ACCELERATION (2) on a velocity time graph You re slowing down.
REPRESENTING NEGATIVE ACCELERATION (2) on an acceleration time graph You re slowing down.
OBJECTS AT REST (1) on a position time graph You re not moving
OBJECTS AT REST (2) on a velocity time graph You re not moving
OBJECTS AT REST (3) on an acceleration- time graph You re not moving
SUMMARY: POSITION A B C D SPEEDING UP SLOWING DOWN CONSTANT VELOCITY (ORIGINAL DIRECTION) CONSTANT VELOCITY (OPPOSITE DIRECTION)
SUMMARY: VELOCITY A B C D SPEEDING UP SLOWING DOWN CONSTANT VELOCITY (ORIGINAL DIRECTION) CONSTANT VELOCITY (OPPOSITE DIRECTION)
SUMMARY: ACCELERATION A B C D SPEEDING UP SLOWING DOWN CONSTANT VELOCITY (ORIGINAL DIRECTION) CONSTANT VELOCITY (OPPOSITE DIRECTION)
INTERPRETING GRAPHS QUESTIONS PAGE 215
Velocity (m/s) INTERPRETING GRAPHS 80 60 40 20 0-20 -40 Velocity-time graph B C A D F 0 1 2 3 4 5 6 7 8 9 10 11 + EAST - WEST ACTIVITY 6 PG. 220-221 -60-80 Time (s) E
INTERPRETING GRAPHS HOMEWORK Exercise 18 pg. 221-228 No. 1-3
TB. PG 234 SAFETY ON OUR ROADS South Africa has very high statistics for road accidents. Why???
ROAD RAGE TB. PG 234
DRUNK DRIVERS TB. PG 234
TIREDNESS TB. PG 234
RECKLESS DRIVING TB. PG 234
LACK OF ATTENTION TB. PG 234
BAD VISIBILITY TB. PG 234
CARS THAT ARE NOT ROADWORTHY TB. PG 234
BAD QUALITY ROADS #ANC TB. PG 234
TB. PG 234 EQUATIONS OF MOTION These are so awesome
We can determine an objects position by.
We can determine an objects velocity by.
We can determine an objects acceleration by.
TB. PG 229 OR We can use equations of motion
Physical Quantity Symbol SI Unit Vector/Scalar Displacement x m Vector Acceleration a m. s 2 Vector Initial Velocity V i m. s 1 Vector Final Velocity V f m. s 1 Vector Time taken t m scalar These equations only apply to movement in a straight line. Only constant acceleration. TB. PG 229
THERE ARE 4 EQUATIONS 1. (m. s 1 ) Final velocity acceleration (m. s 2 ) V f = V i + a t Initial velocity (m. s 1 ) time (s) TB. PG 229
THERE ARE 4 EQUATIONS 2. (m) Displacement acceleration (m. s 2 ) x = V i t + 1 2 a t2 Initial velocity (m. s 1 ) time (s) TB. PG 229
THERE ARE 4 EQUATIONS 3. Final velocity (m. s 1 ) acceleration (m. s 2 ) V f 2 = V i 2 + 2a x Initial velocity (m. s 1 ) displacement (m) TB. PG 229
THERE ARE 4 EQUATIONS 4. Displacement (m) x = (V f V i ) Final velocity (m. s 1 ) 2 Initial velocity t (m. s 1 ) time (s) TB. PG 229
HOW TO USE THESE EQUATIONS 1. What am I given? 2. What do I want to find? TB. PG 229 3. What equation am I going to use? 4. Are my values in the correct units? Write on board EQUATION SUBSTITUTE CALCULATE ANSWER with DIRECTION
EXAMPLES Turn to page 270 Formula Sheet Table 2: MOTION
TB. teacher PG 230 EXPLANATION EXAMPLE A car is waiting at a traffic light. The robot goes green and the motorist accelerates for 10 seconds at 4 m. s 2. 1. Calculate the top speed of the car. 2. How far does the car travel in the first 10 seconds.
TB. pupil PG 230 EXAMPLE 1 A car starts from rest and accelerates in a southern direction at 3m. s 2. 1. Calculate the velocity of the car after 10 seconds. 2. Calculate the distance covered in the 10 seconds. 3. Calculate the average velocity of the car.
TB. pupil PG 230 EXAMPLE 2 A motorbike rider is riding at 40m. s 1 east when he needs to brake for a red traffic light. He needs to stop within 200m. 1. Calculate his acceleration. 2. Calculate the time it will take him to rest.
pupil EXAMPLE 3 A car is travelling at a constant velocity of 20m. s 1 on a long, straight road. The driver suddenly sees a man standing in the middle of the road 140m away from the car. It takes him 2 seconds before he slams on brakes. 1. Calculate how far the car travels during the 2 seconds before the driver applies the brakes. 2. Calculate the minimum acceleration the car will need to stop in time. 3. Calculate the total time taken to come to a stop from the moment the driver saw the man.
THINGS TO REMEMBER starts from rest comes to a stop V i = 0 m. s 1 V f = 0 m. s 1 speeds up / accelerates a = + slows down constant velocity a = a = 0 m. s 2 TB. pg 235
HOMEWORK SFGSDFGSDFG EXERCISE 19 PG. 236-238