Force

Davidson Students Volunteer for ScienceTraining Presentation

Spring, 20117th Grade

Overview

• This lab is broken up into two parts as seen on slideshare. They review force and friction in the following ways:– Measuring Force– Measuring And Experimenting w/ Friction– Forces That Turn A beam

• In this slide show are three different activities pertaining to force . There may be a chance that you will not get to the activities dealing with friction. Keep an eye on the clock. If this happens to be the case, wrap up the lab in an appropriate place.

Definition of Force

• Force- an influence on a body or system that causes that body or system to move, change directions, or change shape.

Preliminary Questions• Ask the students the following questions to assess their

general knowledge of force:

• What is a force?

• What is a force able to do?

• Is force visible?

• After asking the above questions, provide examples of everyday use of force i.e. opening a door, lifting an object, etc.

Effects Of A Force

• One volunteer should loop a rubber band around each index finger and stretch the rubber band. (While doing this, ask the class what happens to the elastic band when a force is applied to it)

• Another volunteer should be assembling the following stand:

= Paper clipSmall piece of white paper taped to stand

Assembly• This assembly requires two screws, a screwdriver, a large, wooden block

with 2 holes, and a smaller wooden block with a fulcrum.

Partially insert screws into the two large holes

Sit the vertical piece on top of the large wooden block and finish screwing in the screws (there are 2 holes in the bottom of vertical piece).

Finished assembly

Fulcrum

Effects Of A Force Cont.• Attach a piece of paper to the the stand behind the elastic band.• Hang rubber band from fulcrum and measure how long the band is when no

weights are hung from it.• BEFORE YOU MOVE ON, ASK THE CLASS TO HYPOTHESIZE WHETHER OR NOT THE

ELASTIC BAND WILL STRETCH BY THE SAME AMOUNT, OR BY DIFFERENT AMOUNTS, IF ACTED UPON BY FORCES OF DIFFERENT SIZES.

• Hang a weight from the paper clip on the rubber band. • Mark the paper at the point the rubber band reaches.• Measure how far the rubber band reaches from the original point.• Record data in a table (see below) on the board.

• Repeat the above process until a total of five weights are hanging from the paper clip.

• Make sure to measure the stretch distance from original point not the previous point!

Effects Of A Force Cont.• After recording all measurements, plot the data on a graph

(see below) and connect the points.

• The graph should show that the stretch in the rubber band will increase with increased weight.

• Disassemble the stand. You will need the large wooden block for the next portions of the lab!!

Measuring Force

• Address the following problem to the class:– We know that when we lift, push, or stretch an object (in

the case of the rubber band), we are exerting a force. How can we measure the size of a force?

The answer to the above question is that a spring balance can be used to measure the size of a force by seeing how much it stretches the spring.

Using The Spring Balance

• The spring balance measures force in Newtons.

• Draw a chart like the one below on the board.

• Under the list of objects, list small wooden block and large wooden block (the small stone will not be used).

• First, estimate the size of the force needed to lift both the large and small wooden block and list the estimates in the chart.

• Second, insert the golden hooks into the small and large wooden blocks by simply screwing them in.

Using The Spring Balance

Using The Spring Balance

• Hang each block from the spring balance and record the measure forces in the chart.

• Pull the same objects across the table top• Measure the force needed to pull and record in

the chart.

Result

• Ask the class if more force is used to lift or pull an object?– By looking at the chart on the board, they should

be able to conclude that more force is required to lift an object.

– The reason for this is that lifting an object has to combat the force of gravity while pulling an object does not have to combat gravity as much due to friction.