Inititally, the pistonn is in thermal equilibrium with a large water bath whose temperature remains constant.. Action: Lock the piston head in place. Remove the piston from the water bath and plunge the piston into very cold water. Enter the signs of W , Q , and U . Use + , , or 0 separated by commas. For example, if W is positive, Q is negative, and U is zero, you would type +,-,0