6.10. What to Remember from Lesson#
This has been a big lesson with lots of ideas. Here’s what we’ll refer to in lessons to come.
6.10.1. Force and Acceleration#
The T-shirt equation, Newton’s 2nd little-l law is simple and we’ll not require any sophisticated or tricky use of it:
If there’s a force on an object, then that object will accelerate. The larger is the mass of an object, the more force is required to accelerate it, or the smaller will its acceleration be. All common-sense ideas nicely packaged in this simple model for acceleration.
6.10.2. Mass and Momentum#
Mass is the resistance to being accelerated—its nickname is inertia. You knew that, but now Newton’s 2nd law embodies it:
big \(m\), small \(a\).
Momentum is the oomph that an object moving at a speed has. It’s a little bit of mass and a little bit of velocity and together they make momentum:
6.10.3. Weight#
Still going with \(F=ma\), but now for a particular acceleration, that of gravity near the surface of the Earth. That force is nearly constant and so the acceleration is nearly constant and we give it a special name, \(g\)…”little gee.” It’s actual value is \(g=9.8\) m/s\(^2\) but we can often get away with using \(g=10\) m/s\(^2\) and I’ll do that whenever I can.
6.10.4. Circular Motion#
The model for circular motion will recur a number of times. Just remember that
or its alter-ego,
which has the merry-go-round experiences encapsulated in this one-line formula. If the force is constant, for any object “making a turn” (or in an orbit!), the further it is from the center of its circular path, the faster it will go. For everyday life, where the centripetal force responsible for keeping an object moving in a circle (tires, seat belts, jeans-on-the merry-go-round, the rope overhead). These frictional or tension forces have a limit and when that’s reached, straight line motion is the result! We’ll encounter circular motion with a force that’s not constant, you just wait.
But first, let’s bang things together.