## Thursday, April 16, 2020

### Virtual Lab: Force, Distance, Work, and Energy

Important background information can be found here:

http://billonscience.blogspot.com/2017/04/concepts-of-force-work-and-energy.html

The lab will provide 3 trials in which force and distance are measured. Using the equation for work,

W = Fd

where W is work, F is applied force and d is distance through which the force was applied

it is relatively simple to calculate how much work was done.

Introductory science students should remember that when two variables are placed beside each other without any operator, it is meant for them to be multiplied.

The lab will provide an initial distance and a final distance that will be used to calculate distance.

The measures in the video are hypothetical, but reflect realistic quantities. They are contrived for the sake of creating a virtual lab experience that do not require actual lab access.

Instructions:

The virtual lab draws from the data in this video:

https://youtu.be/HbOrAmFhKH0

Watch the video and use the data within to complete the lab. The following link should open a COPY of a Google Doc into which you can type your answers.

## Wednesday, April 8, 2020

### Newton's Second Law and Motion: Finding Force

In this article, the topic is the relationship between Newton's Second Law and Motion, and the displacement of an object.

The method here will demonstrate how to find the force needed to move an object.

How do you find the force needed given time (t), final displacement (df), initial displacement (di), initial velocity (vi), and the mass of the object?

Once again, it is necessary to combine two principles in order to see the full relationship.

You will have to find the rate of acceleration (a) using the distance equation, then use that to find the force (F).

So, you want to use

F=ma

to find F, but you don't have the a. That means finding a using the distance information given and the distance equation.

The distance formula is:

df =  di  +  (vi )(t)+ 1/2(a)(t2)

So, we'll be doing two steps.

Step 1:

Use the distance equation to find a:

df =  di  +  (vi )(t)+ 1/2(a)(t2)

Step 2:
Then use the calculated a with Newton's Second Law

F = ma

to find the force.

EXAMPLES

Example 1

Let's take a look at another example (even easier!) and work it out:

What force acts on a object with a mass of 10 kg, if it begins 5 meters from a mark and has an initial velocity of 25 m/s, and ends up a final distance of 227 m from the mark after an elapsed time of 6 seconds?

STEP 1

Find a where:

df = 227 m
di = 5 m
vi = 25 m/s
t = 6 s

df =  di  +  (vi )(t)+ 1/2(a)(t2)
227 m = 5 m + (25 m/s)(6 s) + 1/2(a)(62)

Combine some terms... and PEMDAS

227 m = 5 m + (25 m/s)(6 s) + 1/2(a)(6 s)2
227 m = 5 m + 150 m + 1/2(a)(36 s2)
227 m = 155 m + (18s2)(a)

Subtract 155 m from both sides...

78 m = (18s2)(a)

Divide both sides by 18s2 ...

78 m / 18s2 = a

4 m/s/s = a

Next, use THAT calculated a to find the Force (step 2 above):

Find F where

m = 10 kg
a = 4 m/s/s

F = ma
F = (10 kg )(4 m/s/s)
F = 40 N

Example 2

How about seeing one worked out?

NOTE
While this example shows how to find F when given distance information, the same process applies when asked to find the force given velocity information. However, you'd begin (Step 1) using the velocity information and formula to find a, the go on to Step 2 and solve for force.

SUMMARY:

You gotta do it in steps!

This process requires doing the work in steps. Depending on what is given, you use the two formulas below:

F = ma
df =  di  +  (vi )(t)+ 1/2(a)(t2)

So, read the problem, write down what is being looked for, write down what is given, THEN... use the two formulas. Two steps!