Physics & Kinematics The study of an objects motion in terms of it’s change in position, velocity and rate of change
Read page 340 together • BT Global Challenge Yacht Race (started in 1970) is a race “around the world” (54,000 km) • 12 boats are used (all the same, so that the race really does test the sailors skills) • Relying on wind, boats can obtain speeds of 50km/hr or spend days travelling at 10km/hr. • Along the way in the race, the distance, time and speed of the boats are recorded and their positions are monitored by race officials.
Sailors have to be VERY aware of their changes in speed and position or else they can get very of-course – or find themselves dead last – or possibly even dead. • Each day the crew has to make adjustments to their heading since the speed and direction of the wind and ocean currents can change very quickly • An understanding motion is crucial.
What happens when you get Physics wrong?? • In 1999, NASA lost one of it’s Mars Space orbiter probes in the Martian atmosphere (it cost more than $300 million). • Why?? One group working on the Probe used SI units (meters and Kilograms) and the other group working on it used feet and pounds. • As a result – the computers on the probe made errors in the calculations for putting it into orbit!
Important Tips in Physics: Tip#1: Direction makes a difference!!! • If a classmate invites you over to their new house for a Science study group and tells you that he lives 1 km from the school and that if you walk 4 km/h, it will take you 15 min to get there… Will you be able to find your way?? • NO!!! You need a direction! • His directions would be SCALAR: quantities that describe magnitude but not direction • We want directions that are VECTORS : quantities that describe magnitude and also direction. Eg. Walk 4km/hr east of the school for 15 min
Tip #2: Writing Scalars and Vectors • Scalars are written normally showing no arrows or direction • Eg. 10 km • Vectors show an arrow above them or the direction in brackets • Eg. 10 km [E] - 10 km east
Tip #3: Know some important Vocabulary • 1) DISTANCE: a scalar quantity that describes the length between 2 points or locations • Eg. The Odometer in a car keeps track of the distance you drive. If you start with 50,000km already driven by your car and you go to the movie theatre 10 km away – the odometer reading increases by 10km to 50,010
2) POSITION: a vector quantity that describes an objects location from a reference point. • Eg#1: “I am 3 km east of Orchard Park Mall” • Eg#2: You drive 10 km East to the mall, and then return home. Your distance is 20km travelled, but your position relative to home is 0km (because you are back at the place you started)
3) TIME: Describes when an event happens • 4) TIME INTERVAL: the difference between the initial time (when the event began) and the final time (when the event ended) • Symbol: t (pronounced “delta” t) • Measured in seconds • So time interval describes how long an event was. The t = 14 seconds burp
Calculating the Time Interval • Say a skateboarder is travelling at 1m/sec, and you want to know How long it takes him to travel in a straight line from the fire hydrant to the sign. • Remember, the time he starts by the fire hydrant is his initial time (ti) and the time when he hits the sign is the final time (tf)
t = tf- ti t = 5s- 2s t = 3s • During the 3 second time interval, the skateboarders position has changed – what seems to be the reference point? • The Tree. • Question: So what is the Skateboarder’s position at t = 5s? • 7 m [E] of the tree
5) DISPLACEMENT: a vector quantity, the straight line distance & direction from 1 point to another. (How much an object’s position has changed) • Symbol: d • Measured in meters (m) • Displacement is found by the final position minus the initial position or d = df - di • Question: What’s the Displacement for the skateboarder from the hydrant to the sign? →
During the 3 second time interval, the skateboarders displacement is 5m [E]. The distance travelled was 5 m d = df- di d = 7m[E]- 2m [E] d = 5m [E]
Tip #4: Watch for Signs! West East Left Right + - South North Down Up + -
Think you got it? Try This… • What is the Distance she travelled? • What is the time interval? • What is her Displacement? D=14 m t = 10 sec d = 14 m [W]