Scientific secondary school Course: technological First class

1. Scientific secondary school Course: technological First class Place:classroom and physics laboratory. Title: MOTION UNDER A CONSTANT FORCE Rossana Viola e Maria Bortoluzzi

2. Skills: to make sense of phenomena students observe and interpret information from a variety of sources. To use appropriate scientific terminology to communicate their conceptual understanding. Present scientific information in written, oral, diagrammatic and graphic forms. Carry out investigative work. Present analyses and evaluations of scientific data in appropriate form. Rossana Viola e Maria Bortoluzzi

3. Prerequisites: contents lenght, time, mass, vectors and vector algebra, equations, s-t v-t a-t plots, particle, reference frames and coordinate systems, trajectory and time-law, velocity, acceleration, Straight line motion with a constant speed, covered space as area in a v-t graph. Rossana Viola e Maria Bortoluzzi

4. Module planning Rossana Viola e Maria Bortoluzzi

5. MOTION UNDER A CONSTANT FORCE MOTION WITH A CONSTANT ACCELERATION Rossana Viola e Maria Bortoluzzi

6. VOCABULARY: • Velocity: vettore velocità. • Speed: modulo del vettore velocità. • Grade: pendenza di una retta in un sistema di riferimento (piano cartesiano) • Air-bearing rail: rotaia a cuscinetto d’aria. Rossana Viola e Maria Bortoluzzi

7. Rossana Viola e Maria Bortoluzzi

8. Butthey are difficult motions to describe because of their irregular speed variations ! Rossana Viola e Maria Bortoluzzi

9. There is a naturalmotion in which speed variation in time is almost regular:it’s the motion of drop of a body close to the earth’s surface It may be described in a simple enough way! Rossana Viola e Maria Bortoluzzi

10. In figure a sphere drop is represented. • It has been photographed at equal intervals t= 0.05 s. • In following intervals t the distance covered by the sphere is notconstant but it progressively increases. Rossana Viola e Maria Bortoluzzi

11. Activity: • AIM: represent in a speed - time plot the values of average speeds of the sphere in considered intervals t calculated through the relation : Rossana Viola e Maria Bortoluzzi

12. Speed and time are directly proportional quantities !! Rossana Viola e Maria Bortoluzzi

13. We know that Thus we obtain the speed-time relation: with a = constant. If and that relation becomes or, in general, v=aּt with a = constant. Rossana Viola e Maria Bortoluzzi

14. v = aּtis the equation of the line in previous graph. a is the grade of that line: the greater the acceleration is, the greater the grade will be. For example: Rossana Viola e Maria Bortoluzzi

15. acceleration-time plot The graph is a time axis parallel segment. At time variation, acceleration takes the same value. Rossana Viola e Maria Bortoluzzi

16. We know that in a speed-time plot the area A under the line represents the distance covered by the point in motion in considered time interval. A Let’s deduce thespace-time relation: area A is but v=at, thus therefore time law Rossana Viola e Maria Bortoluzzi

17. Activity Represent the space-time plot Rossana Viola e Maria Bortoluzzi

18. Activity Represent the space-time plot It’s a parabolic curve. There’s a quadratic relation between space and time Rossana Viola e Maria Bortoluzzi

19. exercise Complete following text with some of the words at the bottom of this slide. According to ………’s second law, F=ma, if the …… acting on a particle remains constant in magnitude and direction, the point will move in a ………… with a constant acceleration. This means that the point will acquire equal increments of velocity in equal …………… . Galileo force Newton space time intervals parabolic curve Giuseppe straight line Rossana Viola e Maria Bortoluzzi

20. exercise Complete following text with some of the words at the bottom of this slide. According to ………’s second law, F=ma, if the …… acting on a particle remains constant in magnitude and direction, the point will move in a ………… with a constant acceleration. This means that the point will acquire equal increments of velocity in equal …………… . Galileo force Newton space time intervals parabolic curve Giuseppe straight line Newton force straight line time intervals Rossana Viola e Maria Bortoluzzi

21. exercise A car moves and in 5 seconds covers a distance s=100m. Assuming that the car has a constant acceleration, calculate the value of acceleration and than the speed at the end of these 5 seconds. Rossana Viola e Maria Bortoluzzi

22. exercise A car moves and in 5 seconds covers a distance s=100m. Assuming that the car has a constant acceleration, calculate the value of acceleration and than the speed at the end of these 5 seconds. Rossana Viola e Maria Bortoluzzi

23. Laboratory experiment Aim: to study a straight line motion with a costant acceleration. Equipment: air-bearing rail. Gathered data: space (s) and time (t). Data processing: calculation of speed (v), acceleration (a) and mean value of acceleration. Make a table with all these values. Required plots: 1) space-time 2) speed-time 3) acceleration-time. Rossana Viola e Maria Bortoluzzi

24. What to do:1) make a REPORT.2) fill in a GOWIN CONCEPT MAP like this: Methodological side Theoretical-conceptual side Focal request: Concepts: Evaluation statements: Knowledge statements: Theory: Data processing: Equipment: Gathered data: Event: Rossana Viola e Maria Bortoluzzi

25. What to do:1) make a REPORT.2) fill in a GOWIN CONCEPT MAP like this: Methodological side Theoretical-conceptual side Focal request: How to study a straight line motion with a constant acceleration? Evaluation statements: At the start it’s better push the truck with an electromagnetic device than manually. Concepts: s, t, v, a Theory: v=at s=1/2 at^2 Error theory Knowledge statements: a(m)=…… Data processing: Calculation of v, a, a(m). s-t v-t a-t plots Equipment: Air-bearing rail Gathered data: s,t Event: The truck slides on the rail. Rossana Viola e Maria Bortoluzzi