The Force and Newton's Law of Motion.pptx

Force, Mass, Weight

1. Force and Newton's Law of Motion

2. OBJECTIVES At the end of this lesson, you will be able to: differentiate contact and non-contact forces ; apply Newton’s 1st law to obtain quantitative and qualitative conclusions about the contact and non-contact forces acting on a body in equilibrium; define inertial frames of reference; and distinguish mass and weight. 2

3. WHAT IS A FORCE? - is a push or pull of an object. It is an interaction between two objects or between an object and its environment. Force is a vector quantity, it has magnitude and direction. In most cases, it is denoted by the variable F.

4. WHAT IS THE UNIT OF FORCE? Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is denoted by the variable N and is equivalent to the product of a unit mass multiplied by a unit acceleration as shown:

5. FORCE SCALAR OR VECTOR? force is a vector quantity. Therefore, a force has a magnitude and direction . For forces which are directed towards the primary directions, their sign convention is: + positive when directed upwards or to the right. - negative when directed downwards or to the left.

6. FORCE SCALAR OR VECTOR? •forces with their magnitude and below: direction can also graphically as shown

7. NET FORCE OR RESULTANT FORCE 8 • Free body diagram is the sum of all the forces that act on the system

8. BALANCED VS UNBALANCED FORCES Unbalanced forces - forces that cause a change in an object's motion Balanced Forces - forces acting on an object that do not cause change in the object's motions. (net force=0)

9. CONTACT AND NON-CONTACT FORCE Contact Force - these are forces that involve physical contact between bodies. Non-contact Force or Action-at-a-distance Force - these are forces that do not involve physical contact between bodies

10. CONTACT AND NON-CONTACT FORCE CONTACT FORCE Applied Force Normal Force Friction Force Tension Force Spring Force NON-CONTACT FORCE Air/Fluid Resistance (Weight) Electrical Force Magnetic Force Force Gravitational Force

11. Applied Force (F ) app Applied force is the force applied to an object by a person or another object.

12. Normal Force ( F or N) N The normal force is the support force or reaction force exerted upon an object that is in contact with another stable object. The normal force is always perpendicular to the surface.

13. Friction Force (F)f Friction occurs when a surface resists the sliding of an object. It is always parallel to the surface and directed opposite of the motion.

14. Tension Force ( F or T) t Tension is a pulling force exerted on an object by a rope, string, cord, or chain. It is always a pull and never a push kind of force.

15. Air/Fluid Resistance Force (F ) air/fluid The air/fluid resistance is a special type of frictional force that acts upon objects as they travel through the air. This air resistance is sometimes called drag force and fluid resistance is sometimes called buoyant force.

16. Gravitational Force or Weight (F or W) grav The pull of gravity on an object and is also called weight. It is the force of gravity with which the earth, moon, or other massively large object attracts another object towards itself. Since the earth is round and the center is inside it, the direction of the weight is always downward.

17. Magnetic Force (F ) mag The magnetic force is the attraction or repulsion that arises between electrically charged particles because of their motion. Magnetism is closely related to electricity.

18. ISAAC NEWTON’S LAW OF MOTION Sir Isaac Newton was a physicist and mathematician who developed the principles of modern physics, including the laws of motion and is credited as one of the great minds of the 17th-century Scientific Revolution.

19. Newton’s Laws of Motion Newton’s First Law: Objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by an unbalanced force. Newton’s Second Law: Force equals mass times acceleration (F = ma). Newton’s Third Law: For every action there is an equal and opposite reaction .

20. Newton’s First Law An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force.

21. Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force. If the object was sitting still, it will remain stationary . If it was moving at a constant velocity, it will keep moving . It takes force to change the motion of an object.

22. What is meant by unbalanced force? If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes.

23. Some Examples from Real Life Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion. A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

24. Newton’s First Law is also called the Law of Inertia Inertia : the tendency of an object to resist changes in its state of motion The First Law states that all objects have inertia . The more mass an object has, the more inertia it has (and the harder it is to change its motion).

25. Newton’s Second Law Force equals mass times acceleration. F = ma Acceleration : a measurement of how quickly an object is changing speed.

26. What does F = ma mean? Force is directly proportional to mass and acceleration. Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force. Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

27. What does F = ma say? F = ma basically means that the force of an object comes from its mass and its acceleration. If you double the mass, you double the force. If you double the acceleration, you double the force. Doubling the mass and the acceleration quadruples the force. (2m)(2a) = 4F So . . . what if you decrease the mass by half ? How much force would the object have now?

28. Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force. Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.

29. Newton’s Third Law For every action there is an equal and opposite reaction.

30. For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force . This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

31. Vocabulary Inertia: the tendency of an object to resist changes in its state of motion Acceleration: •a change in velocity a measurement of how quickly an object is changing speed, and direction Velocity: The rate of change of a position along a straight line with respect to time Force: Push or Pull (strength or energy)

32. FRAME OF REFERENCE? A frame of reference is a coordinate system relative to which the position and motion of a object may be described. To find the position of an object can we use frame of reference.

33. INERTIAL REFERENCE FRAME Inertial frame of reference is any frame in which an object remains either at rest or at a constant velocity unless another force acts upon it.

34. Inertial frame of reference A frame of reference which obeys Newton laws of motion is called Inertial frame of reference. Also called Galilean, Newtonian frame of reference.

35. In Newton second law, F= ma If force applied on the body F= 0, then acceleration produced by the body is zero a=0. but mass is not equal to zero. This inertial frame is also known as non accelerating frame. Inertial frame is also called Non rotating frame in case of rotational motion.

36. Non inertial frame of reference A frame of reference which doesn't obeys Newton laws of motion is called non inertial frame of reference. Non inertia means the frame of reference which doesn't moves with uniform velocity. Here acceleration of the body is not equal to zero.

37. WEIGHT NOTE: g may varies on the location of the problem . A cceleration due to the gravity of the EARTH is 9.8m/s 2 or 32ft/s 2 and the acceleration due to the gravity of the MOON is 1.6m/s 2 or 5.3ft/s 2

38. MASS Mass is a measure of matter (inertia) • Mass depends on the number and kind of atoms. • The mass of an object is the mass of an object regardless of where the object is. • Units: Kg

39. EXAMPLE 1 If Ivan goes to the Moon (g What is Ivan's weight if he weighs 55 kg? =1.6m/s2), what will be his new weight? moon