Newton's Second Law of Motion

So this week we did a lab regarding Newton's Second Law of Motion, which states that the acceleration of an object is directly proportional to the force (or net force) on an object. However, the acceleration of an object is an inverse of the mass. The lab we did proved that when we did separate trials of differing mass on the cart vs the hanging mass. The changing force had a direct relationship, while the changing mass had an inverse relationship. So today's post has a picture of my dog, who is proving this rule with the force of touch on her and the acceleration of the wagging of her tail. The more *and harder* you push her or pet her, the more her tail accelerates. She's very light, with little mass, so it's easier for her to accelerate in comparison to a larger, thicker dog.

Free-Body Diagrams

Last week I gave you an introduction to forces and examples of what they do. So today I'm going to show you how to draw a free-body diagram based on a given situation. In the photo above, my friends are on an upward incline (a hill.) Therefore, there are three forces acting on them at any given time— mg (weight), normal force, and friction (keeping them on the hill.) To draw this, you would do this:

This shows that my friends are on the hill and are staying there due to three kinds of forces. I didn't know that free-body diagrams would help me to understand how to do my PA homework problems, but they really do! They also work with other objects, like cars, cartoon characters, balls, rocks, boxes, and Nutter Butters.

Forces

This week we learned about forces... we've moved on from kinematics! (Cue applause here.) We learned that a force is defined as a push or pull. There are two kinds of forces— contact forces, and 'at a distance' forces. Contact forces are caused by contact between 2 objects. You might be thinking, "So these objects are moving." WRONG! Not necessarily. Contact forces don't necessarily cause movement. In fact, contact forces could be just as simple as me and my friend putting our arms around each other for a picture, like in the photo above. 'At a distance' forces are forces that push and pull on objects without touching them. One of the most obvious of these forces is gravity. (SOMETHING FROM KINEMATICS— Gravity= 9.8 m/s2.) These are balanced forces. However, there are also unbalanced forces, also known as net forces. These forces are those that cause an acceleration of an object. A good example of this is when you push a bowling ball down a lane. We're going to be doing a lot with these forces— we'll be implementing them into Newton's First Law of Motion— objects in motion will tend to stay in motion unless acted upon by an outside, unbalanced, force. That's like when you push a person off a cliff and they continue to fall until a spaceship with a scoop net saves them and stops their fall.

Quarter 1 Extra Credit

My mom comments on the blog...

Adding Up The Vectors Graphically or Component-ly

So this week we learned about adding vectors graphically and using the component method (Bureku technique). This is a picture of me flying above Kailua (the Mokuluas are in the background). And NO, it's not Photoshopped. Pinky promise.

So if I am flying 300m north, then 400m east, how can I find the resulting vector? I can find it using the graphical method: creating a scale (100m=1cm in a drawing, etc) and drawing and measuring my distance, then creating a separate resulting vector that happens to be my HYPOTENUSE of the two original vectors. Then, I can measure the resulting vector and convert it. (I would get 500m, by the way.) Or you could use the component method, which involves going in and taking the sin and cos of the resulting triangle in order to solve for the hypotenuse.

But either way, it doesn't change the fact that I am FLYING! :) Yay...