Chapter 3 Motion in a straight line ( Chap. 1 page 3)

1. Chapter 3Motion in a straight line(Chap. 1 page 3) Dr. Haykel Abdelhamid Elabidi February 2014/3rd-4th weeks of RaT 1435

2. Units of Chapter 1 • Measurements, Standards and Units • Displacements, Average Velocity • Instantaneous Velocity • Acceleration • Finding the Motion of an Object • The Acceleration of Gravity and Falling Objects

3. 1- What is Physics • Physics is the study of the fundamental laws of nature. These laws can be expressed as mathematical equations. • It is the science of measurements and experimental. • Physicist (scientist who studies Physics) observes the phenomena of nature and try to find patterns and principles that relate these phenomena.

4. Measurements, Standards and Units • A quantitative discussion of motion requires measurements of times and distances. So we must first consider the standards and units. • All mechanical quantities can be expressed in terms of some combination of three fundamental dimensions: • Length (L), Time (T) and Mass (M). • Example: a velocity is a distance divided by a time and its dimension is L/T. • In Physics, when we speak of the dimension of a physical quantity, we refer to the type of quantity in question, regardless of the units used in the measurement. For example, a velocity measured in km/h and another velocity measured in miles per hour both have the same dimensions L/T.

5. Measurements, Standards and Units • We have to define the unitsusedwhenmeasuring the threequantities: • SI(International System of Units) • or mks(m: meter, k: kilogramand s: second) • Two other systems can be used: • The CGS system: C (centimeter), G (gram), S (second) • The English system: feet (ft), pound (pnd), second (s)

6. Converting units

7. Converting units

8. Converting units

9. Position, Distance, and Displacement • Mechanics is the study of how objects move, how they respond to external forces, and how other factors, such as size, mass and mass distribution affect their motion. • All physical objects will be treated as point particles. Before describing motion, you must set up a coordinate system – define an origin and a positive direction.

10. Position, Distance, and Displacement The distance is the total length of travel; if you drive from your house to the grocery store and back, you have covered a distance of 8.6 mi. Distance is always positive.

11. Average Velocity Description of motion needs to consider how rapidly an object moves. This canbedone by introducing the averagevelocity ([L]/[T]): The averagevelocity tell us how fast an objectismoving and the directionthe objectismoving.

12. Average Velocity

13. Instantaneous Velocity The instantaneousvelocityis the velocity at a particular instant in time. The instantaneous velocity is determined by computing the average velocity for an extremely small time interval.

14. Instantaneous Velocity

15. Average acceleration Like the position, the velocitycan change with time. The rate at which the velocity changes iscalledacceleration: If the acceleration is in the same direction as the velocity, the speed increases. In the opposite case, the speed decreases.

16. Instantaneous acceleration

17. Motion with constant acceleration Different equations for motion with constant acceleration: Example 1.16 page 14 A car initially at rest at a traffic light accelerates at 2 m.s-2 when the light turns green. After 4 s. What are its velocity and position? Solution Example 1.16 page 14

18. The acceleration of gravity and falling objects Free fall is the motion of an object subject only to the influence of gravity positive direction positive direction

19. The acceleration of gravity and falling objects Example 1.20 page 17 A ball is dropped from a window 84 m above the ground. a) When does the ball strike the ground? b) What is the velocity of the ball when it strikes the ground? Solution Example 1.20 page 17

20. Homeworks: Exercises 1.2.; 1.3.; 1.16. and 1.50. pages 21/24 Thank you for your attention See you next time Inchallah