Relative Motion - Motion on Different Perspectives
- 1. Checking Your References Relative Motion
- 2. RELATIVE MOTION Relative motion refers to how the movement of one object appears when compared to another object. It's all about the viewpoint or perspective. For example, if you’re sitting in a moving car, from your perspective, you’re not moving relative to the car, but to someone standing outside, you and the car are both moving. So, the motion of an object can look different depending on where you're observing it from. In short, relative motion is how fast something seems to move, depending on where you're looking from.
- 3. Do you feel like you are motionless right now? ALL Motion is RELATIVE! The only way to define motion is by changing position… The question is changing position relative to WHAT?!? You are moving at about 1000 miles per hour relative to the center of the Earth! The Earth is hurtling around the Sun at over 66,000 miles per hour! MORE MOTION!!!
- 4. Example #1 • A train is moving east at 25 meters per second. A man on the train gets up and walks toward the front at 2 meters per second. • What is his velocity? – Depends on what we want to relate his speed to!!! • +2 m/s (relative to a fixed point on the train) • +27 m/s (relative to a fixed point on the Earth) vtrain = +25 m/s vperson = +2 m/s
- 6. A boat is trying to go straight across the river. Calculate the magnitude of the boat’s velocity relative to an observer on the shore. The velocity of the boat is 0.75 m/s and the velocity of the river is 1.20 m/s
- 9. Calculate
- 12. Example #2 • A passenger on a 747 that is traveling east at 230 meters per second walks toward the lavatory at the rear of the airplane at 1.5 meters per second. • What is the passenger’s velocity? – Again, depends on how you look at it! • -1.5 m/s (relative to a fixed point in the 747) • +228.5 m/s (relative to a fixed point on the Earth)
- 13. Non-Parallel Vectors • What happens to the aircraft’s forward speed when the wind changes direction? vthrust No wind – plane moves with velocity that comes from engines vwind Wind in same direction as plane – adds to overall velocity! Wind is still giving the plane extra speed, but is also pushing it SOUTH. Wind is now NOT having any effect on forward movement, but pushes plane SOUTH. Wind is now slowing the plane somewhat AND pushing it SOUTH. Wind is now working against the aircraft thrust, slowing it down, but causing no drift.
- 14. Perpendicular Kinematics • Critical variable in multi dimensional problems is TIME. • We must consider each dimension SEPARATELY, using TIME as the only crossover VARIABLE.
- 15. Example • A swimmer moving at 0.5 meters per second swims across a 200 meter wide river. 200 m vs = 0.5 m/s How long will it take the swimmer to get across? t d v t =0 The time to cross is unaffected! The swimmer still arrives on the other bank in 400 seconds. What IS different? • Now, assume that as the swimmer moves ACROSS the river, a current pushes him DOWNSTREAM at 0.1 meter per second. vc= 0.1 m/s The arrival POINT will be shifted DOWNSTREAM!