GET FOCUSED

• Students will perform experiments to explore the effect of different surfaces on friction.
• Students will measure frictional force with a spring scale.
• As students perform their lab experiments, they should keep the following question in mind:

How can the force of friction be measured?

How does the force of friction change with surface type?

INVESTIGATE

Trial 1

In Trial 1, students will investigate the frictional force present when a woodblock is pulled along at a constant speed, over the lab table. Students will attach the spring scale to the woodblock and pull it at a constant speed. It is important that students read the spring scale when the woodblock is moving at a constant speed

a. Measure a 30 cm pathway using the metric ruler. Mark the beginning and ending using masking tape.

b. Place the wood block on the table so that it lies on its largest side.

c. Place the elastic band around the sides of the woodblock.

d. Equilibrate the spring scale.

e. Hook the spring scale into the elastic band, so that the Newton scale faces upwards.

f. Place the 100 g weight onto the top of the woodblock.

g. Pull the woodblock at a constant speed. Start the wood block about 10 cm before the start line, and continue to pull the woodblock smoothly along the tabletop until it has gone past the end line.

h. Group members should read the spring scale while the woodblock is pulled smoothly between the start and finish lines. Read the spring scale when the woodblock is moving at a constant speed, not when it speeds up or slows down.

i. Record the force in the Table in Problem 4i of your Student Data Record.

j. Repeat steps 4g through 4i two more times. Record data in the Table in Problem 4i.

Trial 2

Measure frictional force between the woodblock and masking tape.

a. On the table, place three 50 cm long strips of masking tape side by side, sticky side down. Make sure the three strips are touching and that there are no ridges.

b. Use a metric ruler to measure and then draw lines to indicate the beginning and end of a 30 cm runway on the masking tape.

c. Pull the woodblock and 100 g weight along the masking tape runway using a spring scale.

d. Record the force, while the block is moving at a constant speed, in the table above.

e. Repeat two more times. Record the data in the table on the previous page.

Trial 3

In Trial 3, repeat Trial 1 with sandpaper on the tabletop surface.

a. Remove the masking tape.

b. Turn the sandpaper over so that the rough side is facing the table. Tape the two pieces of sandpaper together.

c. Turn the sandpaper over again and tape the sides of the sandpaper to the table.

d. Use a metric ruler and masking tape to indicate the beginning and end of a 30 cm runway on the sandpaper.

e. Pull the woodblock and 100 g weight along the sandpaper using a spring scale.

f. Record the force, while the block is moving at a constant speed, in the table above.

g. Repeat two more times. Record the data in the Table in Problem 4.

Trial 4

In Trial 4, students begin to explore the relationship between weight and the frictional force present when an object moves over a surface. In this Trial, students will record the weight of various configurations of objects. Students will use the spring scale to record the weight in Newtons (N), remembering that the weight in Newtons is equal to the force of gravity on an object.

a. Hook the spring scale to the hole in the handle of the white bucket.

b. Hold up the white bucket and record the weight of the bucket in Newtons using the spring scale. Input the weight of the white bucket into the table below.

c. Place the woodblock (with an elastic band) and papa gram bear into the white bucket and record the weight of the bucket, woodblock, and bear.

d. Remove the papa gram bear and place the metal cube into the bucket. Record the weight of the white bucket, woodblock, and metal cube.

e. Remove the metal cube and place the 100 g weight into the bucket. Record the weight of the white bucket, woodblock, and metal cube.

f. Record your data in Problem 7e.

Trial 5

In Trial 5, students continue their exploration of variables that influence frictional force, by measuring the frictional force of a woodblock and gram bear combination. This is the combination of objects with the least weight out of the three combinations students will test. Students will use the spring scale to determine the frictional force on the woodblock with a papa gram bear on it when moving over the sandpaper.

a. Use the sandpaper pathway as in Trial 3.

b. Hook the spring scale to the woodblock using the elastic band.

c. Place the gram bear on the woodblock.

d. Pull the woodblock along the sandpaper.

e. Record the force from the spring scale, in the Table in Problem 8e.

f. Repeat two more times.

g. Remove the papa gram bear.

Trial 6

In Trial 6, students will continue their exploration of the frictional forces present when a woodblock with a metal cube placed on it, moves over sandpaper. This is the combination of objects with the second greatest weight out of the three combinations students will test. Students will use the spring scale to determine the frictional force.

a. Place the metal cube on the woodblock.

b. Pull the woodblock along the sandpaper.

c. Record the force in the Table in Problem 8e.

d. Repeat two more times.

e. Remove the metal cube.

Trial 7

In Trial 7, students will continue their exploration of the frictional forces present when a woodblock with a 100 g weight placed on it, moves over sandpaper. This is the combination of objects with the greatest weight out of the three combinations students will test. Students will use the spring scale to determine the frictional force.

a. Remove the metal cube. Place the 100 g weight on the woodblock.

b. Pull the woodblock along the sandpaper and determine the force on the spring scale, as you did in Trial 6.

c. Record the force in the Table in Problem 8e.

d. Repeat two more times.

KEYS

CLEAN UP

Let students know your expectations for clean-up. Ask them to clean up.