Q20. Why do balloons expand when filled with air?

Or

Why does the balloon get inflated?

Or

What makes a balloon get inflated when air is filled in it?

Q21. Explain why, a wide steel belt is provided over the wheels of an army tank.

Q22. What is pressure?

Q23. Which force makes a rolling ball stop on its own?

Or

Why a ball rolling along the ground gradually slows down and finally comes to rest?

Or

What makes a ball to stop when it is rolling?

Or

Why does a moving ball stop?

Q24. What is muscular force? Give one example.

Q25. What is described as a change in its state of motion?

Q26. What is meant by a contact force? Give an example.

Q27. Explain, why magnetic force is said to be a non-contact force.

Q28. Why do the shape and size of balloon change when filled with air or water?

Q29. Why water comes out more slowly from an upstairs tap than from a similar tap downstairs?

Q30. Why are we not crushed by atmospheric pressure?

Or

If the pressure due to atmosphere is so great, then why are we not crushed by it?

Q31. What is frictional force?

Or

What is friction?

Q32. Why does a sharp knife cut better than a blunt knife?

Q33. What is meant by atmospheric pressure?

Q34. Give two examples of contact forces.

Q35. A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Q36. What is meant by a non-contact force? Give an example.