Physics Fun with Unit One is Done

We've reached the end of the first unit of Physics that we'll cover this year in class. So far we've covered inertia/Newton's first law, net force and equilibrium, velocity, acceleration and using a graph to solve problems. '

Inertia/Newton's First Law

Newton's first law states that an object in motion will remain in motion and an object a rest will remain at rest unless acted upon by an outside force. This is a property known as inertia. This is a concept applicable to daily life. It can be observed when someone leaves their coffee mug on top of their car. First, the car and the coffee mug are at rest. However, when the car begins to move, the coffee mug falls over. The answer lies in Newton's first law of motion. Since the mug was at rest before the car moved out from underneath it and no outside forces acted upon it, the mug remained at rest and thus fell due to the force of gravity. Another example of this is the tablecloth trick, as shown in the video below.



Net Force and Equilibrium

The net force is the total of all the forces acting on an object. Any time there is a net force, the object is accelerating. For instance, if there is a box being pushed with 6N to the right and 4N to the left, the net force is 2N. This is because the 4 cancels out and then there are two N left over.

There are two instances in which equilibrium occurs: when the net force is 0N and when an object is moving at constant velocity. Therefore, if a box is being pushed upon with 5N to the right and 5N to the left, they cancel out and the net force is 0N. That means that the box is at equilibrium. An object moving at constant velocity is also at equilibrium. That would be like our hovercraft experiment where we moved at a constant speed in one direction without any force from a push or pull.

This is a great video demonstrating other real life examples of equilibrium and net force by some classmates.



Velocity

Velocity can be defined as the distance traveled divided by the time passed.

Velocity, measured in meters per second (m/s) is relative to change in direction and change in speed. Therefore, if a bicycle moves forwards at a constant speed, the bicycle is moving with constant velocity. However, there are three ways that the bicycle's velocity could change:

• If the bicycle is moving at a constant speed, but turns around a corner, the bicycle's velocity will change.
• If the bicycle is moving forward and speeding up, its velocity will change.
• If the bicycle is moving forward and slowing down, its velocity will change.

When dealing with problems involving constant velocity, there are two major types of questions. There are questions looking for distance traveled and questions looking for the velocity.

• How far ? These are questions looking for the distance traveled (m) these will be solved using the equation distance equals velocity multiplied by time, or d=vt.
• How fast? These are questions looking for the velocity (m/s) and will be solved using the equation velocity equals distance divided by time, or v=d/t.

These can also be rearranged to find the time.

This is a video I made with my classmates about these topics.



Acceleration

Acceleration can be defined as the change in velocity divided by the time passed. Acceleration is measured in meters per second squared, or m/s^2.

There are three ways to recognize acceleration:

1. change in direction
2. speeding up
3. slowing down.

Note that these three things are also what cause change in velocity. Therefore if an object is accelerating, it does not have constant velocity. Acceleration is not possible with a constant speed, unlike velocity.

Acceleration is different from speed in the sense that there can be an object with increasing velocityand decreasing acceleration. What that means is that as the object rolls down a ramp its velocity is increasing, but it is increasing by smaller increments as it goes. A toy car could have a speed of 1m/s then after one second the velocity could be 2.5 m/s, but after another second goes by, the velocity could be 3 m/s. That indicates that while it is still speeding up, the rate at which it is speeding up is decreasing.

There are two types of questions asked  about acceleration. There are questions looking to find the distance and there are questions looking to find the acceleration.

How far ? These are questions looking for the distance traveled (m) these will be solved using the equation distance equals one half multiplied by the acceleration multiplied by time squared, or d=1/2at^2.

How fast? These are questions looking for the velocity (m/s) and will be solved using the equation velocity equals acceleration multiplied by time, or v=at.

These can be rearranged to find acceleration and time as well.

This is a handy video explaining acceleration and its units.



Using a Graph to Solve Problems

A graph can be used to show constant velocity or constant acceleration. In these graphs, the distance (m) will always be on the y-axis and the time (s) will always be on the x-axis. A graph for constant velocity will have a straight line. If everything is not squared for the constant acceleration graph, it will produced a curved line.

The first step is to look at the information and see what is missing. Looking at what is already provided by the graph will give a hint as to what is missing. The slope will be equal to whatever is missing. For example, if the equation of the graph is y= 3.8651x + 0.2 (if b is close to zero, disregard it) and you know from the graph that the time is squared, it is simple to find out what the slope represents. Writing out the equation in words makes it easier to identify these parts: the distance is equal to the slope (3.8651) multiplied by the time squared. And since you know that the time is not just seconds but seconds squared, it is clear that the equation is d=1/2at^2. With that information, you know that the slope represent half of the acceleration, because it is the only part of the equation that the graph has not provided you with. In order to find the acceleration, you multiply the slope by 2 and then fill it into the spot where 1/2a would be in the formula.

This video explains how these graphs work.