Electricity and Magnetism

The Force How can the strength of the force of attraction between two magnets be measured? From earlier observations, we thought that the force of attraction didn’t work if the magnets were too far apart. How could we be sure that observation is true?

Getters: 1 magnet-on-a-post 1 magnet 1 balance 2 plastic cups 1 bag of washers

The Investigation Your group is to conduct an investigation to determine how much force is needed to pull the magnets apart. We must agree on a standard procedure for measuring force between the magnets, so everyone can work on the problem the same way following the same set of instructions. Using a balance, figure out how many washers would break the force of attraction with the magnets.

Refining the Procedure Does it make a difference where you place the washers in the cup? Does it make a difference how you place the washers in the cup? At random or stacked for example? Does it matter if you drop the washers into the cup? Do you get the same results if you set up the equipment in the same way and do several tests (multiple trials)? Write down the steps in your science notebook. Reporters: Once your group has found out how many washers it takes to break the force, report your group’s results.

Investigation Question What do you think will happen to the force of attraction between two magnets if you put a plastic spacer between the two attracting magnets? Do you think the force will get stronger, weaker, or stay the same?

Procedure Getters: one plastic spacer Retest the number of washers needed to break the force with no spacers, then find out how many washers are needed to break the force when one plastic spacer is placed between the two attracting magnets. The spacer is easiest to handle if it is placed on top of the magnet-on-a-post. Remember to conduct multiple trials.

Assessing Experimental Techniques Use the same technique each time a washer is placed in the cup. Place the cup gently. Try to reset the balance each time the force is broken.

Recording Data on the T-Table Use notebook sheet # 6 The Force. Use the information we already gathered and record it on the graph.

Inquiry I am going to give each group five additional spacers so you can continue your experiments. But I don’t want you to test two spacers now. Skip over two spacers and test three, four, five, and six spacers. Leave a place for two spacers in your T-table, but DON’T TEST TWO SPACERS YET!

Graphing the Results How many spacers did you use in the investigation? Write the numbers 0-6 on the horizontal axis and label it “Number of Spacers” Number the lines 0 to 20 on the vertical axis and label it “Number of Washers.” Record your data from the T-table on the graph.

Make Predictions Using the Graph Where is the greatest difference between the numbers of washers it took to break the force? Where is the least difference? Can you predict the number of washers needed to break the force when two spacers are placed between the magnets? Use multiple trials to test your predictions.

Discuss Results How many washers did it take to break the force with two spacers. How many spacers were used when it took four washers to break the force? How can you use a graph to predict? Which is more helpful to use in predicting the number of washers it will take using two spacers, the T-table or the graph?

Vocabulary Graph A graph organizes data visually to show a relationship between two things. Prediction (pre- means before; -diction means speak) A prediction is an educated guess based on data or previous experience. To predict is to make an educated guess. Intersection The intersection of two lines is the point at which the cross. Multiple Trials In a scientific investigation you should do multiple trials (three or more) to confirm your results.

Content What happens to the strength of attraction between two magnets as the distance between them increases? The greater the distance between two magnets, the weaker the force of attraction.