The terms weight and mass are often used incorrectly. Phrases like ‘a bag of sugar weighs 1 kg’ are not scientifically correct. This means that a 1 kg mass would be attracted to Earth by a force of 10 ...

Activity 1 – Order the surfaces – How much friction do they produce? Activity 2 – Moving things quiz Activity 3 – Solve this problem Activity 4 – Conduct an investigation We need forces to make things ...

November 24, 2025 • Our annual reading guide returns with 380+ new titles handpicked by NPR staff and trusted critics. Find 13 years of recommendations all in one place — that's more than 4,000 great ...