Darla and Rob plan an investigation to see if adding weights to a car affects its speed down a ramp. Their experimental setup consists of a ramp made of a piece of wood that is 30 cm long. The ramp is propped up on four books to give it a height at one end of 8 cm. What is the independent variable in this investigation?

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

firearm identification is the process of analyzing the bullets and cartridge cases left at a crime scene to determine if they came from a particular firearm. marks on the bullets and cartridges may be common to every firearm of that type. these are called class characteristics.