Unit 01 Resources

Big Idea

AN OBJECT WILL RETAIN ITS CURRENT STATE OF MOTION -- INCLUDING BOTH ITS CURRENT DIRECTION AND SPEED -- UNTIL ACTED UPON BY AN UNBALANCED EXTERNAL FORCE.

Objects in our everyday experience tend to slow to a stop due to the forces of friction and air resistance. Eliminating these forces reveals that objects will continue to move as they are moving right now. Objects resist changes in this motion, due to their inertia -- a feature of the object's mass.

What should I know?

1. The position of an object can only be determined by reference to some other point -- called a reference point.

2. This position is really a distance away from that reference point in a particular direction.

3. In this class, distances are nearly always measured in meters.

4. As in all sciences, observations in the form of measurements must be both as precise and as accurate as possible. Precision is reported as a measurement's number of significant figures, and accuracy is often reported as a percent error.

5. The choice of a reference point is up to the observer. It should be chosen in a way that makes the most sense for the observer or that makes future observations the easiest to analyze.

6. The set of all the positions and motions of objects from a particular reference point is called a frame of reference.

7. Motion is observed when an object's position -- the distance and direction it is from a reference point -- changes in a particular frame of reference.

8. It is possible for an object to move in one frame of reference but not move in another frame of reference.

9. Constant motion in a frame of reference occurs when an object's position changes by the same amount and in the same direction in equal units of time.

10. Objects at rest in a given reference frame are also considered to have constant motion. Being "at rest" means that the object is not moving in that reference frame.

11. In this class, time is nearly always measured in seconds.

12. The distance that an object covers in a second is called that object's speed.

13. The change in the object's position -- both its distance from a reference point and its direction from that reference point -- is called its velocity.

14. Speed and velocity are not synonyms: speed is a scalar measurement -- one that does not require a direction, and velocity is a vector measurement -- one that does require a direction.

15. Unbalanced forces -- pushes or pulls on the object -- are required to change the motion of an object.

16. It is the natural state of objects that are not experiencing any unbalanced forces to move with a constant velocity. 

17. Objects will resist changes to their velocity in an amount that is proportional to their mass. This property is known as inertia.

18. The greater the mass of an object, the more difficult it will be change its velocity. This means that it will be harder to slow it down, to speed it up, or to turn it.

19. In this class, mass is nearly always measured in kilograms.

20. The base units of meters, kilograms and seconds make up the foundation for the MKS system of units, which includes nearly all the units we will use in this class.

21. NEWTON'S FIRST LAW OF MOTION -- also called the Law of Inertia -- states that objects resist changes in their velocity until they are acted upon by an unbalanced force.

Vocabulary

1. Inertia -- the resistance to changes in motion. The amount of this resistance is based on the amount of mass in the object, because each atom resists a change in its motion. The more atoms, the more total resistance to a change in motion.

2. Force -- an interaction between objects that attempts to cause a change in motion. In other words, a push or a pull.

3. Scalar Quantity -- a measurement that does not take a direction, e.g. time or temperature.

4. Vector Quantity -- a measurement that requires both a magnitude (size) and a direction, e.g. force or displacement.

5. Vector -- an arrow drawn to represent a vector quantity. The length of the arrow shows the relative magnitude of the measurement. The direction in which the arrow points is the direction in which the vector quantity is acting.

6. Vector Addition -- a method that uses geometry to add two vector quantities of similar type.

7. Resultant -- the vector result of the combination of two or more vectors through vector addition.

8. Net Force -- the vector sum or resultant force remaining after all forces acting on an object are added using vector addition.

9. Law of Inertia -- also known as Newton's first law of motion. It states that every object continues in a state of rest or of uniform speed in a straight line unless acted upon by a net force.

10. Mechanical Equilibrium -- sometimes called translational equilibrium. It is the state of an object or system of objects for which there are no changes in motion.

11. Equilibrium Rule -- for an object or system of objects to be in mechanical equilibrium -- in other words, for them to remain at rest or for their motions to be constant -- the sum of all the forces acting on an object must be zero. Another way of saying this is that objects that do not experience changes to their motion of any kind have no net force acting on them.

12. Distance -- the total amount of length traveled in any direction. This is a scalar quantity.

13. Displacement -- a measure of an object's change in position -- including both a length measurement and a direction. This is a vector quantity.

14. Speed -- the distance traveled in a unit of time. It answers the question "how fast..." It is a scalar quantity.

15. Instantaneous Speed -- the speed at a particular moment in time. This is what is seen on the speedometer of your car.

16. Average Speed -- the speed over a period of time. This the result your get when you divide the total distance traveled by the total time it takes to travel that distance. Note that it does not tell you exactly what speeds were traveled during that period, but simply gives you an average.

17. Velocity -- the speed traveled in a direction. Because it requires a direction, this is a vector quantity.

18. Constant Velocity -- the state in which neither the speed nor the direction of motion changes.

Notes for This Unit

Sample Problem Videos

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