Travis notes that his prediction is significantly lower than his calculated velocity. which error explains this difference? a) he forgot to account for friction. b) he forgot to zero the balance and found a weight for the marble that was too low. c) he weighed the marble in a weighing dish and failed to account for the mass of the weighing dish. d) he didn't position the photogate correctly and got the time required for the top of the marble to pass through, rather than to the middle.