ICP

1. ICP Describing Motion

2. Introduction • Everything around us is in motion. People walk, run, ride bikes, or drive. The earth rotates and orbits the sun. • The sun is also moving around the Milky Way Galaxy which is also moving through space. • Even the particles of atoms are moving. • Since motion is common to everything in the universe, it is essential to study how it works.

3. What is motion? • Motion is based on observation. • When an object changes position with respect to a frame of reference, the object is in motion.

4. Frame of Reference: Motion is relative to where you are in relation to the object in motion Reference Point: A point to begin in making a measurement (the zero point) Distance: how far something has moved (the length of the path the object took) Displacement: the straight line distance and direction of the motion Position and DistanceKey Terms

5. Three Ways to Describe Motion • Language—Common words can describe motion in sentences. • Mathematical equations. • Graphs show how quantities involving motion change over time.

6. Speed VS Velocity • Speed describes how fast an object moves. • Velocity describes how fast an object moves and the direction it is moving. • Speed is a scalar and velocity is a vector. • Velocity could be either positive or negative.

7. Scalar: a quantity having only magnitude. Ex: distance Vector: a quantity having both magnitude and direction. Ex: displacement or placement w Scalar VS Vector

8. Examples of Scalars and Vectors

9. How do we measure velocity or speed? • To calculate speed, we need to measure the distance traveled and the time it took to travel that distance. • Velocity just adds the direction: is it in the positive direction or negative?

10. Example Problem • In the 1988 Summer Olympics, Florence Griffith-Joyner won the 100-m race in 10.54 s. Assuming the length of the race is measured to 0.1 m, find her average velocity in m/s. • Dx =+100.0 m 100.0 m/10.54 s • Dt = 10.54 s = 9.488 m/s or 9.5 m/s

11. Instantaneous Velocity • Instantaneous velocity is the velocity at a given time. • We can investigate the relationship between distance and time in many ways. • Mathematical equations and graphs are good representations of distance and time.

12. Position-Time Graphs • A graph that shows how position depends on time is called a position-time graph. • Time is the independent variable and is graphed on the x-axis. • Position is the dependent variable and is graphed on the y-axis. • The slope of the graph is the average velocity.

13. Constant Velocity=Uniform Velocity • Constant velocity—the average velocity of an object is the same for all time intervals • For a position-time graph, constant velocity is a straight line equal to the slope.

14. Slope Review • Slope is defined as rise over run. • The rise refers to the numbers of the vertical axis; the run refers to the numbers of the x-axis. • The slope, m, in the equation: Y = mx + b, is found by dividing the change in y by the change in x. • The slope of a position-time graph is velocity.

15. Positive and Negative Velocities • Positions can be positive or negative. Positive is to the right of a reference point and negative is to the left of a reference point. • Time intervals, however, are always positive. • Velocity can be either positive or negative depending on if the position is positive or negative.

16. Velocity-time Graph • A velocity-time graph is used to describe motion with either constant or changing velocity. • For constant velocity, the graphed line is parallel to the x-axis.

17. Acceleration • Acceleration is defined as the rate at which velocity changes. • Acceleration is large when there is a large velocity change in a small time interval. • The ratio is called the average acceleration between the 2 times.

18. Acceleration • Acceleration can be a change in speed—either speeding up or slowing down. • Acceleration can be a change in direction (vectors include direction).

19. Acceleration is Relative. Velocity is measure in meters per second, m/s, so acceleration is measured in m/s/s or m/s2. Since position and velocity are vectors, so is acceleration. In straight-line motion, acceleration can be positive or negative. Units of acceleration

20. Calculating Acceleration • The velocity of a car increases from 2.0 m/s at 1.0 s to 16 m/s at 4.5 s. What is the car’s average acceleration?

21. Solution • Given: Unknown: a v1 = 2.0 m/s Equation: v2 = 16 m/s t1 = 1.0 s t2 = 4.5 s Solution: 14 m/s= 4.0 m/s2 3.5 s

22. Graphing Accelerated Motion • Acceleration is the slope of a velocity VS time graph. • The slope would be change in velocity (the y value) divided by the change in time (the x value).

23. Fundamental Forces • Scientists identify 4 fundamental forces in nature. • Gravitational force • Electromagnetic force • Strong nuclear force • Weak nuclear force

24. Fundamental Forces Vary in Strength • Strong nuclear force is the strongest but acts only over the distance inside the nucleus of an atom. • The electromagnetic force is 1/100 the size of the strong nuclear. • Gravitational force is weaker and the weak nuclear force is weakest.

25. Field Forces • Some forces, called field forces, can act over a distance. • The attraction of gravity and magnetism are field forces.

26. Balanced and Unbalanced Forces • Whenever there is a net force acting on an object, the object will accelerate in the direction of the net force.

27. Balanced and Unbalanced Forces • Balanced forces do not change motion. • Ex: a light hanging from the ceiling is balanced (if not, it would fall). • Unbalanced forces do not cancel completely. • If 2 students are pushing against each other in the same direction, the forces combine.

28. Force of Friction • Friction is a force that opposes motion. • Friction is what makes an object slow down as it rolls across the floor. • Friction allows us to stand, sit, and walk. • Friction occurs because the surface of any object is rough.

29. Two Types of Friction • 1. Static friction: friction between 2 surfaces that are not moving. • Static friction opposes the start of motion. • 2. Kinetic (sliding) friction: the friction between 2 surfaces that are moving. • Sliding friction is less than static friction but will cause motion to slow down.

30. Friction and Motion • Friction is necessary for many everyday tasks. • Sometimes we need to increase friction: slick roads call for deeper treads on tires to grip the road better. • Sometimes we need to reduce friction: machinery requires oil or grease to decrease friction.

31. Cars could not move without friction • Tires gripping the road (friction) allow our cars to move. • The brake pushing on the tire (friction) allows us to stop and stay in one place. • In order to keep a car moving, we constantly apply force to keep the car moving or friction will make it stop.