Today’s soundtrack is Pistol Annies: Hell on Heels, a modern country rock album.
Everything You Need to Ace Science in One Big Fat Notebook
Chapter 10: Force and Newton’s Laws of Motion
In yesterday’s post, we learned about motion. But we didn’t learn what causes motion, which we will rectify today. Motion is caused by force, which “is a push or pull” (p. 99) that either makes an object move or changes its speed, direction, or shape. We calculate force based on its magnitude and direction.
Often, there will be more than one force at work on an object. When we add up the values of all the forces, we get net force. Of course, if the forces are acting in different directions, we would subtract them from each other instead.
An example of forces acting in different directions could be the act of throwing something into the air. “But wait,” the man in the yellow hat says, “you’ve only mentioned a single force – your throw!” Ah, but there’s more. Did you forget about . . . gravity? And what about the air friction? So we can see that we often have multiple forces acting upon a given object.
Isaac Newton studied force and motion; he gave us three laws of motion that tell us what to expect when forces act upon objects:
1) “‘An object in motion will remain in motion and an object at rest will remain at rest unless there is net force acting on the object'” (p. 101). This means that without friction or gravity in effect, any object that is moved will keep moving, and that unless something moves an immobile object, it will stay where it is indefinitely. This is the idea of inertia: “matter’s resistance to change in motion” (p. 101).
2) “‘The acceleration of an object is equal to the net force on an object divided by the mass of the object'” (p. 103). This means that the more force you apply to an object, the faster it accelerates; also, objects with less mass will accelerate more quickly than objects with more mass will if the same amount of force is applied to each.
3) “‘Forces act in pairs: For every action, there is an equal but opposite reaction'” (p. 105). This law refers to forces that are coupled together, called action-reaction pairs, such as when “you land on the trampoline, and the trampoline exerts an equal but opposite force on you, sending you up into the air” (p. 106).
- The difference between a balanced force and an unbalanced force is that in the former, two forces are acting oppositely and cancel each other out; in the latter, the portion of the larger force that is equal in value to the smaller force cancels out the smaller force, and only the remaining portion of the larger force affects the object
- If two people are playing tug-of-war and one person pulls with a force of 15 N and the other pulls with a force of 10 N, there is a net force of 5 N.
- Newton’s first law of motion is without applied forces, objects in motion will stay in motion, while objects at rest will remain at rest.
- If a 2,000 kg car accelerates at a rate of 3m/s^2, the force that the engine is applying to the car is
222.2 N6,000N, because force = mass times acceleration, which equals 2000 times 3.
- Newton’s second law of motion is that objects with less mass can be more quickly accelerated, and that more force gives more acceleration.
- A “Newton” is a unit of force. One unit is
equivalent to the earth’s gravity at sea levelthe force needed to accelerate an object with a mass of 1 kilogram at 1 meter per second squared.
- Newton’s third law of motion is that for every action there is an equal and opposite reaction.
- When we jump in the air, the reason that we move and the earth doesn’t is because of Newton’s second law: we have much less mass than the earth, so we aren’t generating enough force to move the earth, but we are generating enough force to move us.
Systematic Theology (Wayne Grudem)
Chapter 3: The Canon of Scripture
This chapter addresses the importance of identifying the canon of Scripture, which is “the list of all the books that belong in the Bible” (p. 54). In Deuteronomy 4:2, we are told to neither add to nor subtract from Scripture. The reason for this is, as we learned yesterday, that the Bible is God’s written word, which is the ultimate authority.
The concept of Scriptural canon began with the ten commandments written by God on the two tablets. Next, Moses wrote books, and Joshua after him. Later, other prophets wrote books as they were directed by the Holy Spirit, up until “approximately 435 B.C.” (p. 56), at which time the Holy Spirit ceased to direct writing. Other works were written (the Apocrypha), but even at the time, they were not considered divinely inspired or worthy of being included as scripture. In the New Testament, there are many references to the Old Testament books, but no references to the material found in the Apocrypha. Neither Jews nor Protestants accept the Apocrypha as Scripture, but the Roman Catholic church does, despite the Apocrypha’s “doctrinal and historical inconsistencies” (p. 59).
After Jesus’ resurrection, his apostles were given “an authority equal to that of the Old Testament prophets, an authority to speak and write words that are God’s very words” (p. 61). The majority of the New Testament canon is given to us by “direct authorship by the apostles” (p. 62), and those that aren’t are “self-attesting” (p. 63) in that a reading of them makes clear their divine authorship, in addition to “apostolic endorsement [and] consistency with the rest of Scripture” (p. 63). Ultimately, for any book to be considered canonically Scripture, “it is absolutely necessary that the book have divine authorship” (p. 63).
Will any more books be added to the Bible in the future? No, despite Brian Simmons’ claim to the contrary. We are living in the last days mentioned in Hebrews 1; this tells us that “there is a finality to the revelation of God in Christ and that once this revelation has been completed, no more is to be expected” (p. 64). Revelation 22:18-19 also makes it clear that the Scriptures are closed.
There are two reasons that we can trust that our current canon of Scripture: First, God will preserve His word for us to read. Second, the historical and theological data agrees with it. So there are neither books present in the Bible that shouldn’t be, nor books absent that should be present. As Grudem writes, “God’s faithfulness to his people convinces us that there is nothing missing from Scripture that God thinks we need to know for obeying him and trusting him fully. The canon of Scripture today is exactly what God wanted it to be, and it will stay that way until Christ returns” (p. 69).