Ch 4-6 Notes

1. Ch 4-6 Notes Mr. Russo Beaumont High School

2. Objective: Ch 4.3-4.5 (Pg 40) • We will be able to define inertia and explain Newton’s first law of motion.

3. Ch 4.3 – 4.5 NotesForce • Force – Any push or pull

4. Friction • Friction – Name given to force that acts between materials that touch as they move past each other

5. Inertia • Inertia – Every material object resists change in its state of motion (laziness of an object)

7. Figure 4.3

8. Newton’s 1st law • Newton’s 1st Law (Law of inertia) – Every object continues in a state of rest or of motion in a straight line at constant speed, unless it is compelled to change that state by forces acting upon it. – Newton • An object at rest stays at rest, and an object in motion stays in motion without forces acting upon them

9. This reminds me of you • Students doing math 2 and 3 step math problems

10. Demos • Hanging Mass • Penny in a cup • Paper and bottle

11. Why do objects slow down and stop? • Because of outside forces, mostly because of friction

12. What would happen if you threw an object from a space station? • It would go forever

13. Inertia Explained • The more mass an object has, the more inertia it has. Less mass, less inertia • Is it easier to pick up a toy car or a real car? • Inertia is laziness

14. What is mass? • Mass – The amount of material present in an object • Measure of inertia of an object • MASS DOESN’T CHANGE

15. What do we measure mass in? • Mass is measured in kilograms

16. What is the difference between mass, volume and weight? To calculate weight we use the formula w = m*g g = force of gravity

17. For Example • Mass of boulder = 10 kg • Weight of boulder = 0 kg • Volume of boulder = 10 L

18. On your white board • If a woman has a mass of 50 kg, calculate her weight in Newtons • w = mg • w = (50kg)(9.8m/s2) • w = 490 N

19. On your white board • Calculate in newtons the weight of a 2000 kg elephant • w = mg • w = (2000kg)(9.8m/s2) • w = 19,600 N

20. On your white board • Calculate in newtons the weight of a 2.5 kg melon. What is the weight in pounds? • (4.45 N = 1lb) • w = mg • w = (2.5kg)(9.8m/s2) • w = 24.5 N • 24.5 N / 4.45 N = 5.5 lbs

21. On your white board • An apple weighs about 1 N. What is its mass in kilograms? What is its weight in pounds? (2.2 lbs = 1 kg) • w = mg • 1 N = (m)(9.8m/s2) • m = 1N / 9.8 m/s2 = .1 kg • .1 kg = .22 lbs

22. On your white board • Susie finds she weighs 300 N. Calculate her mass. • w = mg • 300 N = (m)(9.8m/s2) • m = 30.6 kg

23. Objective: Ch 4.6-4.9 (Pg 44) • Given 2 or more forces we will be able to calculate the net force exerted on an object

24. Notes 4.6 – 4.9, Force • Net Force – The combination of all forces acting on an object. • Net force changes an objects state of motion

25. What happens if you pull with equal and opposite forces? • Nothing! • If forces are equal and opposite the net force is zero!

26. What is the minimum # of forces acting on an object at rest? • 2 • Force of gravity (Down) • Normal Force (Up)

27. Normal Force • Normal Force – Upward force on an object • also called the support force

28. Equilibrium • Equilibrium – When all forces on an object cancel out. Net force is zero • Object will not move if at rest

29. Draw Figure 4.11

30. Tension Force • Tension Force – When atoms are stretched • (As opposed to being compressed)

31. When the angle from vertical increases, what happens to the tension force? • Tension always increases as the angle away from vertical increases

33. Slogan: • Net Force is zero, of course – Tanner • Do you move – Jose • Net Force Zero, no excuses – Mia • Equilibrium equals net force zero – Michael • Are you in motion – Tim • Chuck Norris & Mr Russo, Net force ZERO! – JJ • Net Force is zero, unless your Chuck Norris - Chris

34. What happens if you flip a coin in an airplane while its moving? • It behaves as if the plane were at rest. Why? • Inertia

35. Objective

36. Ch 5.1-5.4 - What must happen for acceleration to occur? • Forces cause acceleration • Hockey Puck at rest • No Acceleration • Player hits puck • Acceleration • Puck moving across ice • No acceleration

37. Acceleration is directly proportional to what? • Acceleration is directly proportional to the Net Force acting on it • More force = more acceleration • Less force = less acceleration

38. Newton’s 2nd Law • Newton’s 2nd Law – The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the object. – Newton • More Force = More acceleration (Directly Related) • More Mass = Less Acceleration (Inversely Related)

39. What is the formula for acceleration? • Acceleration = Net force / Mass • More commonly • F = ma • a = F/m • m = F/a

41. What are the units for the Newton • Force is measured in NEWTONS • Force is mass x accelerationUnits are kg*(m/s2)

42. Friction • Friction – between two objects touching. • Always acts in direction opposite to state of motion

43. Fluids • Fluids – Gases or liquids ( because they flow)

44. Air Resistance • Air Resistance – Friction acting on something moving through air

45. How can acceleration be zero when there is still a force applied? • When there is a force applied, the force of friction will balance it out and make net force zero

46. Pressure • Pressure - force per unit area • P= F/A

48. Terminal Speed / Terminal Velocity • Terminal Speed - Object is falling and no longer is accelerating • Terminal Velocity – Same thing, direction is down

49. Ch 6.1-6.6 If you push against a wall, how come it doesn’t fall over? • Because the wall is pushing back on you.

50. Interaction • Interaction – A mutual action between objects where each object exerts equal and opposite forces