4 examplels of chemical change?

Assume you measured the mass of the cart to be (500 ± 1) g and the mass of the additional mass you put on the cart to be (500 ± 1) g as well. since the scale you are using in the lab cannot measure objects heavier than 600g you will have to sum up individual pieces and propagate the error. so what would be the mass and the standard error of the cart and the mass

Language is not the only way that humans communicate. describe how we use sound, touch, chemicals, and sight to communicate. need answer asap

Due in 40 explain in terms of frame of reference if you’re inside a moving train everything on the outside can seem to be moving