For a science experiment what are some safety reasons for having a partner?

Which of the following statements are incorrect?

An engineer decides to use a slightly weaker material rather than a stronger material, since she knows that the stronger material can break suddenly. this is an example of what? a choosing a material that will show warning before it fails b using composite materials that combine strength c using a material for multiple applications d using design techniques that increase efficiency and reduce cost

Two like-charged particles are placed close to each other. how would the force of repulsion be affected if the charge on one of the particles is doubled and that on the other is reduced to half the original value?