Physics

1. Physics Science AS1.6

2. Topics to be covered Energy Work & Power Heat Motion Forces Momentum Electricity NSF North Mississippi GK-8

3. Its about calculations • Don’t panic!! • Read the question CAREFULLY • WHY? • The examiners will often give you the two variables that you need to complete the calculation. • Check your answer – is it reasonable and realistic? If not, you’ve made a mistake!! NSF North Mississippi GK-8

4. Achieve, Merit, Excellence • Achieved questions – purely calculations given the variables. • Merit questions – calculations where you use the variable from the achieved part of the question. • Excellence questions – calculations up to a merit level with some discussion on the effects of different values of the variables. NSF North Mississippi GK-8

5. How it works • You get marks for the whole calculation – • State the formula • State the variables • Do the calculation • Get the answer • Remember the units – the answer is no good without them. NSF North Mississippi GK-8

6. Starter Name three non-contact forces: NSF North Mississippi GK-8

7. Contact vs non-contact forces Contact forces: Touch the object they are acting on • Pushing • Pulling • Twisting Non-contact forces: move something with touching it • Gravity • Magnetic • Electrical NSF North Mississippi GK-8

8. Force • Forces act on us all the time. • We know a force is acting on an object if it deforms or changes the motion of the object. • Force is measured in Newtons (N). • The fractions are worked like the metric system. NSF North Mississippi GK-8

9. If two equal-sized forces act in opposite directions on an object then the net force is zero. The object is said to be in equilibrium. Balanced forces on a body can be recognised when an object is (a) stationary. (b) moving at a constant speed. The forces are balanced, the box does not move NSF North Mississippi GK-8

10. When the action and reaction forces are equal in size and opposite in direction they are said to be balanced. If we increase the force from the right what happens? The forces are now unbalanced, the box moves in the direction of the imbalance and should do so indefinitely in a frictionless environment. NSF North Mississippi GK-8

11. Forces are balanced so the object doesn’t move. Some forces become unbalanced and the object moves in the direction of the extra force. NSF North Mississippi GK-8

12. Movement and unbalanced forces • When the action force is different in size or direction from the reaction force, then the forces are said to be unbalanced. • The resultant unbalanced force always accelerates an object in the direction of the net force. • This means that an accelerating object is always acted on by unbalanced forces. NSF North Mississippi GK-8

13. Calculating the unbalanced force • For forces acting in opposite directions, the unbalanced force can be calculated by subtracting the smaller force from the larger one. • The resultant unbalanced force is in the direction of the larger force. 10 N 35 N 25 N Two opposite forces Resulting unbalanced force NSF North Mississippi GK-8

14. More force rules 80 N + 25 N in the same direction = a single force of . . . 80 N + 25 N in opposite directions = a single force of . . . 55 N + 25 N in one direction and 80 N in the opposite directions = NO MOVEMENT NSF North Mississippi GK-8

15. Forces Gravity Friction Thrust Support NSF North Mississippi GK-8

16. Weight vs Mass • Weight: is the defined as the force of gravity pulling downwards on an object and is measured in newtons • Mass: is measured in kilograms Weight force = mass of object x acceleration due to gravity Fgravity = m x g NSF North Mississippi GK-8

17. Acceleration due to gravity • On the surface of earth the potential acceleration of an object due to force of gravity is 10ms-2 • If your mass on earth is 60kg, the the weight force acting on your body is given by 60kg x 10ms-2 = 600N NSF North Mississippi GK-8

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19. Starter The passengers in a car of mass 1500kg have the following masses; 125kg, 105kg, 95kg, and 75kg • Calculate the total mass of the car and passengers • What would the car and passengers weigh? NSF North Mississippi GK-8

20. Question My puppy Oatis has a weight of 70N. What is his mass? NSF North Mississippi GK-8

21. F m g NSF North Mississippi GK-8

22. Starter NSF North Mississippi GK-8

23. Force, mass, acceleration • If the net force increases the acceleration will also increase. A motor bike can produce much more thrust than a scooter so its acceleration will be greater. • Acceleration is directly proportional to the net force NSF North Mississippi GK-8

24. Force, mass, acceleration • If the mass of an object increases, then its acceleration will decrease. A scooter with a pillion passenger will not be able to drag off a scooter with a single rider. • Acceleration is inversely proportional to mass NSF North Mississippi GK-8

25. The relationship between unbalanced forces and acceleration • This is given by the equation. • Force (F) = mass (m) x acceleration (a) • F = m.a • Force in newtons, mass in kg and acceleration is ms-2 NSF North Mississippi GK-8

26. Example • A toy with a mass of 1.5 kg is pulled by a string and accelerates at 2 ms-1. What is the size of the force? • F=m.a • = 1.5 x 2 • = 3 N NSF North Mississippi GK-8

27. Example • A force of 500 N is used to accelerate a 2 kg object. What is the acceleration? • F=m.a • a = F/m • = 500/2 • = 250 ms-1 NSF North Mississippi GK-8

28. Example • An object accelerates at 7.5 ms-2 when a force of 15 000 N is applied to it. What is the mass of the object? • F=m.a • m=F/a • = 15000/7.5 • = 2000 kg NSF North Mississippi GK-8

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30. Tandem skydiving Ariana is skydiving for the first time Her and her jumpmaster have a combined mass of 150kg • Using Fg = mg find their weight They jump out of the plane, one force acting on them is gravity • Name the other force and state the direction NSF North Mississippi GK-8

31. During the free fall the net force acting on adriana and the jumpmaster is 825N • Calculate their net acceleration. • Discuss how when released the parachute reduces their speed. NSF North Mississippi GK-8

32. Motion This is about the observation, measurement and analysis of moving bodies.

33. Acceleration – an increase in an object’s speed (or direction) caused by unbalanced forces • Deceleration – a decrease in an object’s speed (or direction) caused by unbalanced forces NSF North Mississippi GK-8

34. Distance – time graphs • It is possible to measure the distance of an object as it moves away from a starting position and plot this information on a graph. • This is called a distance-time graph. NSF North Mississippi GK-8

35. Stopped Distance from start (m) Constant speed Constant speed decelerating accelerating Time (seconds) NSF North Mississippi GK-8

36. Stopped Distance from start (m) Time (seconds) NSF North Mississippi GK-8

37. Draw the distance-time graphs for the below • A car traveling at top speed along the motorway • A Mother bird fetching food for its chick • A skateboarder going down a hill NSF North Mississippi GK-8

38. Distance, time, speed • Distance-time graphs give information about the speed of an object. The slope/gradient of a distance-time graph equals the speed. • Different slopes describe differences in speed NSF North Mississippi GK-8

39. Speed and velocity • An object has speed when it travels a distance in a given time. • The formula is:- • Speed (v) = distance travelled (d)/time (t) • v = d/t NSF North Mississippi GK-8

40. Remember to get the units right • Distance is measured in metres (m) • Time is measured in seconds (s) • Speed is metres/second (m/s or ms-1) NSF North Mississippi GK-8

41. VELOCITY The word scientists use to describe how fast an object is moving NSF North Mississippi GK-8

42. Instantaneous and average speed • At any given instant an object has a speed. This is called instantaneous speed. In a car this is measured by the speedometer. • The average speed, is the speed of an object during a given period of time. • It takes into account the many different instantaneous speeds during the journey. NSF North Mississippi GK-8

43. Average speed • The distance becomes the total distance travelled. • The time becomes the total time taken to complete the journey. • An example • The bus to school travels at a number of different (instantaneous) speeds at it stops and starts, but at the end of the journey has traveled at an average speed for the whole journey. NSF North Mississippi GK-8

44. Constant speed • A body traveling at a constant speed is traveling equal distances during a similar time period. • This means that the average speed is the same as the instantaneous speed in this case. NSF North Mississippi GK-8

45. Velocity is measured as: distance travelled over time taken Vaverage = distance time D V T NSF North Mississippi GK-8

46. What are some examples of objects that move at high velocities? NSF North Mississippi GK-8

47. What are some examples of objects that move at low velocities? NSF North Mississippi GK-8

48. What units would you use to measure the velocity of an object moving in this classroom? meters per second m s or ms-1 Meters per second tells us how many meters something can move in one second. NSF North Mississippi GK-8

49. Graphing the Motion of a Particle? NSF North Mississippi GK-8

50. Problems • A traffic officer finds a car has travelled 600m in 20 seconds. What is the average speed of the car • Two snails are being raced in a school lab. Eric went 8cm in 24seconds, while splutter went 12cm in 48seconds. Which snail is faster? • A car is travelling at a constant speed of 30ms-1. How far does it travel in 40seconds • A shock wave from an earthquake travels at a speed of 8kms-1.How long does it take to reach a town 96 km away? NSF North Mississippi GK-8