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# Physics on the Road -Lesson 6

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### Physics on the Road -Lesson 6

1. 1. Relative Velocity Physics on the Road Lesson 6
2. 2. LI…  Add velocities as vectors, tip to tail.  find relative velocity  Identify collision courses
3. 3. What’s the next move?
4. 4. Air Traffic Control At busy airports air traffic control need to track multiple aircraft. Each aircraft is identified and it’s height, distance, direction and speed monitored by radar. Distance 20 km Speed = 100 m/s Distance ? km Speed = 100 m/s What assumptions and variables are important?
5. 5. How do you catch a ball? 1. Keep your eye on the ball 2. Run at the right speed Must keep the angle of your line of sight the same. This becomes trickier as the ball gets closer. The Physics You keep the vector of the relative motion between you and the ball in the same direction.
6. 6. Collision course  Predicting a collision is looking ahead. Computing the next move. A calculation of the future. 1000 km/h 1000 km/h Time to collision = distance approach velocity Approach velocity is the relative velocity how do we work it out? 10 km
7. 7. Collision course 2 1000 km/h 1000 km/h 10 km AvB = vA -vB AvB = vA +(-vB) A B 1000 km/h vA 1000 km/h vB AvB 2000 km/h We are looking at A from B
8. 8. Collision course 3 1000 km/h 1000 km/h Time to collision = distance approach velocity = 10/2000 = 0.005 h = 18 s 10 km
9. 9. Relative velocity  To find relative velocity you subtract the vectors.  That is the same as adding an opposite vector. 225 m/s 212 m/s 225 m/s 212 m/s 2v1 = v2 – v1 2v1 = v2 + - v1 vr If the relative velocity is in a line between the objects… 1 2
10. 10. Are we heading for Xing disaster? 60o