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Year 10

Year 10. May the force be with you!. Types of Force. A contact force requires objects to be touching for the force to have an effect. A field force will act at a distance – the field is the area within which the force has an effect. Types of force. Contact. Field. Magnetic Gravity

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Year 10

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  1. Year 10 May the force be with you!

  2. Types of Force • A contact force requires objects to be touching for the force to have an effect. • A field force will act at a distance – the field is the area within which the force has an effect

  3. Types of force Contact Field Magnetic Gravity Static electricity • Push • Pull • Twist Come up for a example for each.

  4. Forces acting upon objects. Gravity Thrust Friction Support

  5. Results in either no motion or constant motion. Balanced Forces 600N 600N

  6. 600N ↑ = 200N ↑ 400N ↓ Results in acceleration; a change in motion (speeding up or slowing down) Unbalanced Forces

  7. Calculating net force. • The net force is the difference in the amount of force acting upon an object. • The object will move in the direction of the bigger force. • If all forces are balanced the net force will be 0N. 10N 10N 10N 10N

  8. If the forces are unbalanced, there will be a net force acting upon the object. • If the car is moving forward with 50N of force and experiencing 20N of friction pulling it backwards; the net force will be 30N forwards (acceleration). 50N 20N Net force 30N 10N 10N

  9. 40N • If the car is moving forward with 40N of force and experiencing 50N of friction pulling it backwards; the net force will be 10N backwards (reversing). 50N Net force 10N 10N 10N

  10. If the object has two net forces, the movement will go in the direction of the combined net force. • Movement will be forwards and down. Net force 2N 5N 50N 10N Net force 45N 8N

  11. Calculate the net force acting on these objects. A B 5N 55N 20N 25N 20N 5N 5N 5N C D 10N 10N 10N 10N 15N 20N 10N 10N 10N

  12. Distance/time graphs.

  13. d/t graphs

  14. Calculating Forces- using a formula. • To calculate the size of an unbalanced force acting on an object, you need to know its mass and how much it accelerates (changes its speed) due to the net force. • F = ma F ÷ m a x

  15. You can figure out any of the three factors. • Using the triangle! • Cover up the factor you want to calculate. In this case force, the triangle tells you to use; m x a F m a

  16. Need to figure out mass? Now you can use F ÷ a • Need to figure out acceleration? Now you can use F ÷ m F F m m a a

  17. Calculate these equations. • An unbalanced force causes a 1200kg car to accelerate at 2ms-2. What is the size of the net force? • A 0.25kg soccer ball is kicked at 8ms-2. What is the size of the net force? • A 50N force is acting on a skateboard which is accelerating at 5ms-2. What is the mass of the skateboard?

  18. 4. A cart with a mass of 50kg is moved with a force of 100N, what will the acceleration be? 5. A 3000N force is required to move a cannon at 0.5ms-2, what is the mass of the cannon?

  19. Calculate these equations. • 2400N • 2N • 10kg • 2ms-2 • 6000kg

  20. Force = motion? • So as we have seen both balanced and unbalanced forces can result in motion. • When an object moves it changes its location in an amount of time. • In order to work out how fast the motion is occurring, we use the following formula; speed = distance ÷ time d s t

  21. Speed of the trolley. • Once we have recorded the distance the trolley travelled every 0.1s, we can; • Create a d/t graph. • Calculate the overall speed of the trolley. • Calculate the instantaneous speed of the trolley. • Create a v/t graph.

  22. Units of speed. • The two commonly used units for speed are; metres per second (ms-1) and kilometres per hour (kmhr-1). • Sometimes you will need to convert your measurements to fit one of the two units. • E.g. 100km in 30 minutes becomes 100km in 0.5hr= 100/0.5 = 200kmhr-1 • 5km in 30s becomes 5000m in 30s= 5000/30 = 166.6ms-1

  23. Use formula to solve… • A car travels 50km in 30 minutes, what is its speed? • A bus travels 100 km at 50kmhr-1, how long does it take? • A bike travels at 5ms-1 for 5 minutes, how far has it travelled?

  24. Use the formula to solve… • 100kmhr-1 • 2 hours • 1500m or 1.5km

  25. d t Distance/Time Graphs • When drawing distance/time graphs: • Time always goes along the horizontal (x) axis. • Distance always goes up the vertical (y) axis • A flat line (slope = 0) means the object is stationary.

  26. d d t t • A slope means the object is moving.The slope gives the speed of the object. • A curved line means the object is accelerating(speeding up or slowing down).

  27. Drawing a distance time graph. • The distance time graph will show the motion of this car race.

  28. Motion of a car in a race.

  29. Working out speed from a graph. • You can calculate the speed of an object by reading the graph gradient, e.g. rise over run for squares and rectangles. • You can also use the area under the graph for triangles by using ½ base x height. • It’s a bit complex, let’s break it down now…

  30. Experiment; motion of a cart. • Set up the ticker tape timer and physics trolley along the bench.

  31. Measure out 1m of ticker tape timer tape and attach to the trolley. • Accelerate the trolley down the bench and remove the tape. • Rule the tape into 4 dot sections thusly; Start of tape • Number each section from the start of the tape. CV CV CV CV CV CV CV CV CV CV

  32. Create a graph. • Cut each section down the line (through each 5th dot). • Line up along the bottom of the page along the time axis & glue. • Measure the length of each section and record it on the strip.

  33. What does that mean? • You have created a distance time graph for your trolley’s journey. • Now you have the distance for each strip you can calculate the speed for each part of the journey (each paper section took 0.1s). • Use the formula to work out the speed for each section of the journey.

  34. What next? • Speed time graphs! • Speed time graphs show how fast objects are moving over time. s t

  35. Speed/time Graphs • Time always goes along the horizontal (x) axis • Speed or velocity always goes up the vertical (y) axis\ • A flat line (slope = 0) meansthe object is travelling at a constant speed(no acceleration) • A slope means the object isaccelerating. The slope givesthe acceleration of the object • A curved line means therate of acceleration is increasing or decreasing s t s t s t

  36. s/t Speed (ms-1) Time (min)

  37. Turn your trolley data into a s/t graph. Speed (ms-1) Time (min)

  38. Exercise. • Complete the 2 speed/time graphs for the motion of the skateboard and the train.

  39. Acceleration. • Any change in speed is acceleration. • Acceleration = Final speed – Initial speed Time • Speeding up; positive number • Slowing down; negative number

  40. Exercises: show all workings. • A bike starts at 0ms and speeds up to 10ms in 10 seconds. What is the acceleration? • A car starts at 100ms and brakes to 2ms in 20 seconds. What is the acceleration? 1ms-2 -4.9ms-2

  41. Force, Mass & Acceleration • When an unbalanced force acts on an object, it accelerates in the direction of the net force. • The equation is: force = mass x acceleration Fnet = ma • The same equation also applies to the effect of gravity on mass (ie. weight). weight force = mass x acceleration due to gravity Fw= mg = m x10N (if mass is in kg) • The unit for weight force is the Newton (N). Pg 19

  42. F= ma

  43. Friction. Friction is a force that opposes motion. It is created when objects rub against each other, releasing energy as heat. Friction between an object and air or water is called drag. Friction can be: • useful – e.g. brakes, tyres • undesirable – e.g. engine wear Friction can be reduced by using: • lubricants • bearings

  44. Experiment; friction blocks. Aim: To investigate the friction force between different surfaces on a friction block and the bench. Hypothesis: Which side of the block will create the most friction force?On which surface? Method: 1. Attach a force meter to the hook on the block. 2. Put a 1kg mass in your block. 3. Place your block on the bench with the wooden side down. • Pull on the force meter and record the force at which your block starts to move. Repeat 3 ×. • Flip block to second side and repeat, repeat for 2 remaining sides. • Calculate the average force used for each block side on each surface. Results: record your results in a table. Graph: create a graph Conclusion: write a conclusion that links your results to your aim.

  45. Force (N) Block surface

  46. Experiment; shoes. Aim: To investigate the friction force between your shoe and different surfaces. Hypothesis: which surface will create the most friction? Method: 1. Attach a force meter to your shoe. 2. Put a 1kg mass in your shoe. • Place your block on the lino and record the force to move 1m. • Repeat twice more. • Repeat for carpet & concrete. • Calculate the average force used for each shoe on each surface. • Repeat whole experiment with your lab partners shoe. Results: record your results in a table. Graph: create a graph. Conclusion: write a conclusion that links your results to your aim.

  47. Graph: averages only

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