Purpose
This interactive allows you to explore the conditions for the static equilibrium of an extended object.

Using the Interactive

• Configure the interactive using the CONTROLS template on the right-hand side.
• The left-hand side shows a ladder leaning against a frictionless wall; there is friction between the ladder and the ground.
• The arrow at the bottom represents the maximum force of static friction.
• Numerical values can be displayed in a table that appears below the picture of the ladder and the wall.

• Friction: This slider controls the coefficient of static friction between the ladder and the ground.
• Angle: This slider controls the initial angle that the ladder makes with the ground.
• Select Go to see if the ladder will slip or remain in equilibrium; and Reset to place the ladder back against the wall. Step Up and Step Down moves the pail up and down the ladder.
• View: These check boxes are for representing the forces (arrows), the torques (circles), and the tabulated numerical data.
• View Speed: This slider controls the speed of the animation if the ladder slips.

1			Starting with the default setting, deselect the TORQUE VECTORS and VECTOR TABLE boxes and move the VIEW SPEED slider to the far left. Select Go and note that the ladder does not slip. Select Reset. As the angle of the ladder decreases...
			A)	it becomes more likely to slip.
			B)	it becomes less likely to slip.
			C)	it is neither more nor less likely to slip.
2			Noting that the ladder is just barely out of equilibrium, what will happen if I place the pail on the bottom step?
			A)	The ladder will be further out of equilibrium and slip even faster than before.
			B)	The will again be in equilibrium and will not slip.
			C)	The pail will not affect equilibrium, so the ladder will slip just as before.
3			Select Step Up. Select Go. As the pail is moved up ladder...
			A)	it becomes more likely to slip.
			B)	it becomes less likely to slip.
			C)	it is neither more nor less likely to slip.