# Grade 5 Physics: Energy, Force, and Simple Machines

Currently we are in a physics block with my younger daughter (fifth grade.) It is an introduction, because I didn’t feel like I gave it enough attention in years past. Physics has so much one can delve into, that I had a challenging time deciding what to include and what to leave out. So far, I’ve decided that we’ll do the following:

## Energy and Force

We started with energy and force as those two concepts are involved in almost (probably) all of physics. We spent two days on these concepts in conjunction with a little on momentum. Two of my sources are Volumes I and II of Building a Foundation of Scientific Understanding

The first day was probably our most boring day, as we spent it mostly in conversation. For our energy and force units we used exercises C -1 and C-3 in Volume I. Day 2 we played with balls and our Keva blocks in the Contraptions 200 set to make ramps and experiment with balls to discuss momentum.

## Simple Machines

### Lever

Then we moved on to simple machines for a total of three days. First, we experimented with the lever. If you are not aware, there is a relationship between the load and the distance of the fulcrum and the force exerted on the other side of the level and it’s distance from the fulcrum. Load x Distance = Distance x Force or more accurately Force X Distance = Force1 X Distance1.

We used nickels as both our ‘load’ and to measure our ‘force.’ This is a common physics exercise that can easily be found online. It is also an adaptation of the exercise C:11 from Building Foundations in Scientific Understanding, Volume 2. The number of nickels stayed the same on one side – our load – but the distance changed as we moved it incrementally towards the fulcrum (center) of the lever. The distance stayed the same on the other side, but we measured our force in the number of nickels that it took to lift the ‘load.’

This exercise could easily be done without math by just observing the changes (when our load is closer to the fulcrum, it takes less force to lift the same amount,) but we measured the load/force and distance for each side in a chart. We noted when the force changed, and wrote down those measurements. Then we looked for patterns. We are used to looking for different patterns in math (note the Number Sums Curriculum available on my site.) We first added the distance and the force/load for each side, but there was no relationship that we could see. Then we took the difference – still no relationship. Finally, we multiplied the two together. Wa La!! That was our relationship. (F x D = F1 x D1)

We talked about how if we decrease one variable on one side, we have to decrease something on the other, either the force or the distance to even the sides again.

### Pulleys

Completing our work on simple machines and mechanical advantage, we moved on to working with pulleys. There is a great experiment in Building A Foundation, but I opted to just play with pulleys to get an idea of how they worked, so I used group of 5 pulleys, a rope, and a rocking chair – my beloved Amish-made wooden, handmade rocking chair. I was just slightly nervous about this experiment.

First, I had her try to lift the rocking chair by herself. I’m not sure this was really helpful as the size made lifting to be awkward, so I think the ‘work’ in lifting it was missed on her. We have a large eye screw that is in one of our rafters that I attached a double pulley to it. We then ran the rope through one of the pulleys and back down to attach it to the chair. She lifted the chair to see how much ‘work’ was required. From here, we add another pulley to the chair and ran the rope through the pulley in the rafter, down through the chair pulley, back up to the second of the double pulley at the rafters. She again tested the amount of ‘work’ needed to lift it. The amount of ‘work’ was considerably less. We then added a second pulley to the chair, and a third pulley to the rafter. This time we ran the rope from the first pulley at the rafters, down to the first pulley at the chair, back up to the second pulley at the rafter, and down to the second pulley at the chair, and finally back up to the third pully before bringing the rope back down for her to pull. This arrangement was the most obvious in its ease to lift the chair. We talked about our observations and how each pulley decreased the amount of ‘work’ needed to lift the chair.

## Gears

The last day of simple machines was left working with gears. We lightly discussed that gears also gave mechanical advantage, thus making work easier. I contemplated making our own gears, but in the end chose a kit for a clock from US Gears. This was a fun project for her to put together.

Below is a video of some highlight from the first few days of this unit.

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