Motion
Motion An object’s change in position over time when compared to a reference point is called motion. Reference point: The object that appears to stay in place in relation to the object that is moving. Examples: Earth’s surface, buildings, trees, floor Motion is caused by a force acting on a object, this force can be a push or pull.
Describing Motion Direction- movement in relation to the reference point. Examples: North, South, East, West, up, down, left, right Displacement: the total distance traveled from the origin
Scalar or Vector A scalar quantity can be fully described by it’s magnitude (number). EX: mass, temp, length, energy, time, distance A vector quantity requires that both magnitude and direction be described. EX: displacement- 40 ft. North from the origin
Speed: A Scalar Measurement
Determining Average Speed
A graph showing speed
Practice Problems What is the average speed of a car that traveled 300.0 miles in 5.5 hours? How much time would it take for the sound of thunder to travel 1,500 meters if sound travels at a speed of 330 m/sec? How much time would it take for an airplane to reach its destination if it traveled at an average speed of 790 kilometers/hour for a distance of 4,700 kilometers? What is the airplane’s speed in miles/ hour? How far can a person run in 15 minutes if he or she runs at an average speed of 16 km/hr? (HINT: Remember to convert minutes to hours.) In problem 5, what is the runner’s distance traveled in miles?
How far will a you travel if you run for 10 minutes at 2 m/sec? A snail can move approximately 0.30 meters per minute. How many meters can the snail cover in 15 minutes? You know that there are 1,609 meters in a mile. The number of feet in a mile is 5,280. Use these equalities to answer the following problems: a. How many centimeters equals one inch? b. What is the speed of the snail in problem 7 in inches per minute? Calculate the average speed (in km/h) of a car stuck in traffic that drives 12 kilometers in 2 hours. How long would it take you to swim across a lake that is 900 meters across if you swim at 1.5 m/sec? a. What is the answer in seconds? b. What is the answer in minutes? How far will a you travel if you run for 10 minutes at 2 m/sec?
Velocity: A Vector Quantity Remember that vectors require both magnitude and direction. Velocity is a measure of displacement / time in a direction Ex: 4m/s north Velocity always includes a reference direction
Velocity Two birds leave the same tree at the same time. They both fly at 10km/h for 1 hour, 15 km/h for 30 min., and 5 km/h for 1hour. Why don’t they end up at the same destination? They went in different directions.
Types of Velocity Average Velocity: Total displacement / total time in a direction Instantaneous velocity: The velocity at one instant in time
Resultant Velocities When you combine two velocities in the same direction, add them together to find the resultant velocity. When you combine two velocities in opposite directions, subtract the smaller velocity from the larger velocity to find the resultant velocity. The resultant velocity is in the direction of the larger velocity.
Practice 1. Which of the following is an example of velocity? 25 m/s forward 1,500 km/h 55 m/h south All of the above 2. What is a reference point? 3. What two things do you need to know to determine speed? 4. What is the difference between speed and velocity? What kind of quantity is speed compared to velocity? 5. Applied thinking: Why is it important to know a tornadoes velocity and not it’s speed?