Newton’s Laws

1. Newton’s Laws Unit 2

2. Contributors to the theory of motion

3. Aristotle • Divided motion into two types: natural and violent • Natural motion- either straight up or straight down • Violent motion- the result of forces that pushed or pulled

4. Copernicus • Reasoned that the Earth moved around the sun

5. Galileo • Supported Copernicus • Force: any push or pull • Friction: force that acts between materials that touch as the move past each other • Argued that only when friction is present is a force needed to keep an object moving • Inertia: the property of a body to resist change

6. Newton • Developed the famous laws of motion

7. Newton’s First 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 exerted upon it.

9. The more mass an object has, the greater its inertia & the more force it takes to change its state of motion • Mass is different than volume & weight. • mass: a measure of the inertia an object has • Volume: a measure of space • Weight: the force of gravity on an object weight= mass x gravity

10. The combination of all forces acting on an object is called the net force.It is the net force that changes an object’s state of motion.

11. When an object is at rest, forces balance & produce a net force of zero. One force is gravity. The other force is the normal force. This means that the object is in a state of equilibrium.

12. Felicia, a ballet dancer, has a mass of 45kg. What is Felicia’s weight on Earth?What is Felicia’s mass on Jupiter, where the acceleration due to gravity is 25 m/s2?What is Felicia’s weight on Jupiter?

13. A 20g sparrow flying toward a bird feeder mistakes the pane of glass in a window for an opening and slams into it with a force of 2N. What is the bird’s acceleration?

14. A 30g arrow is shot by William Tell through an 8cm thick apple sitting on top of his son’s head. If the arrow enters the apple at 30m/s and emerges at 25m/s in the same direction, with what force has the apple resisted the arrow?

15. Newton’s Second Law Force = mass x acceleration

16. Force causes acceleration.To increases the acceleration of an object, you must increase the net force acting on it.The acceleration depends on the mass.Acceleration is inversely proportional to the mass.

17. Force= mass x acceleration

18. Friction acts on materials that are in contact with each other. It always acts in a direction to oppose motion. The force of friction between surfaces depends on the kinds of materials in contact & how much the surfaces are pressed together.

19. Friction also occurs in liquids & gases. Fluid friction occurs as an object pushes aside the fluid it is moving through. An example is air resistance.When friction is present, an object may move with a constant velocity even when an outside force is applied to it. The friction force just balances the applied force so the net force is zero and no acceleration occurs.

20. Pressure= force/ area of application • The smaller the area supporting a given force, the greater the pressure on that surface. • Measured in pascals (Pa) • One Newton per square meter equals one pascal

22. Galileo showed that objects in free fall accelerate equally regardless of their masses. A 10kg cannonball and a 1kg rock would fall with equal accelerations- 10 m/s.

23. When air resistance is present, a falling object accelerates only until it reaches its terminal speed. At terminal speed, the force of air resistance balances the force of gravity & the net force is zeroAcceleration= weight - resistance

24. Rose is sledding down an ice-covered hill inclined at an angle of 15 degrees to the horizontal. If Rose and the sled have a combined mass of 54kg, what is the force pulling them down the hill?

25. Brian is walking through the school cafeteria but does not realize that the person in front of him has just spilled his glass of chocolate milk. As Brian, who weighs 420N, steps in the milk, the coefficient of sliding friction between Brian and the floor is suddenly reduced to 0.040. What is the force of sliding friction between Brian and the slippery floor?

26. While redecorating her apartment, Kitty slowly pushes an 82kg china cabinet across the wooden dining room floor, which resists the motion with a force of friction of 320N. What is the coefficient of sliding friction between the china cabinet and the floor?

27. At Sea World, a 900kg polar bear slides down a wet slide inclined at an angle of 25 degrees to the horizontal. The coefficient of friction between the bear and the slide is 0.0500. What frictional force impedes the bear’s motion down the slide?

28. Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

29. Newton realized that a force is not a thing in itself but part of a mutual action, an interaction, between one thing & another.In every interaction, the forces always occur in pairs & cannot exist without each other.One force is called the action force. The other is called the reaction force.

30. Action: Object A exerts a force on Object BReaction: Object B exerts a force on Object A

31. Remember that action-reaction force pairs are equal but opposite in strength. We must also take mass into account. A given force exerted on a small mass produces a greater acceleration than the same force exerted on a large mass.

32. Newton’s Third law helps us to explain how rockets are propelled, how helicopters get their lifting force, and how birds and airplanes fly.

33. Since action and reaction forces are equal but opposite, why don’t they cancel to zero?

34. If action & reaction forces are internal to a system, they cancel each other & produce no acceleration of the system. A force external to the system is needed to accelerate the system.

35. Flip, an exhausted gymnast, hangs from a bar by both arms in an effort to catch his breath. If Flip has a mass of 65kg, what is the tension in each of Flip’s arms as he hangs in place?

36. At an art auction, Whitney has acquired a painting that now hangs from a nail on her wall. If the painting has a mass of 12.6kg, what is the tension in each side of the wire supporting the painting?

37. Michelle likes to swing on a tire tied to a tree branch in her yard. If Michelle and the tire have a combined mass of 82.5kg, and Elwin pulls Michelle back far enough for her to make an angle to 30 degrees with the vertical, what is the tension in the rope supporting Michelle and the tire?

38. After returning home from the beach, Samantha hangs her wet 0.20kg bathing suit in the center of the 6m long clothesline to dry. This causes the clothesline to sag 4cm. What is the tension in the clothesline?

39. Brooke comes home from school and puts her books down on the kitchen table while she goes to grab a snack. The books have a combined weight of 25N and the area of contact is 0.19m by 0.24m. What pressure do the books apply on the table?

40. A full coffee mug has a mass of 0.6kg and an empty mug has a mass of 0.3kg. If the full mug applies a pressure of 1200Pa, what is the area inside a circular ring of coffee left on the table by the bottom of the mug?What is the radius of the ring of coffee?