Can you please help me with this conceptual question?

[*best&sweetest*]

What can cause errors in ballistic pendulum lab?
Does friction counts in some of these causes?

[marcusl]

Friction is always a factor in physical systems, but is probably negligible. Can you provide details of your problem? No one here can know what your "pendulum lab" is.

[marcusl]

Please don't assume "usual". I work in industry and don't know your assignment, course, instructor, book, or even if you're in high school or college.

You should think about all sources of variability and error. How accurately do you measure pendulum heights? Masses? Distance to floor impact? Does your spring mechanism release reproducibly every time? You can probably think of more. All of them contribute to variance in the answer.