Question

a student, liam, is sitting on a chair, working on his science lesson.

1. if liam is sitting on the chair, what type of force is he doing?
2. if another student pushed liam off his chair, what two forces are acting on him?
3. if liam pushes himself off the floor, what is his force called?

Explanation:

Question 12

When Liam sits on the chair, he exerts a force due to his weight (gravity - related) on the chair, and the chair exerts a normal force on him. But the force he is "doing" (exerting on the chair) is a contact force, specifically a compressive force or the force of his weight (which is a gravitational - derived force) acting as a downward force on the chair. The main force he is applying to the chair is a downward force, which can be considered a type of contact force (since it's through direct contact) and is also related to gravitational force (his weight). The force he exerts on the chair is a downward force, often called the force of gravity (weight) acting as a force he applies to the chair, or more precisely, a contact force (normal force - like but from his side) where he pushes the chair down with a force equal to his weight. So the type of force he is doing (exerting on the chair) is a downward force, which is a contact force (and related to gravitational force as his weight).

When another student pushes Liam off the chair, first, there is the applied force from the other student (the push force, a contact force). Second, there is the force of gravity acting on Liam, pulling him downwards. Also, if we consider the motion after the push, there might be air resistance, but the two main forces acting on him are the applied force (from the push) and the force of gravity (weight).

When Liam pushes himself off the floor, he exerts a force on the floor, and according to Newton's third law, the floor exerts an equal and opposite force on him. The force he applies to the floor is a push force, and the force that propels him (the reaction force from the floor) is a normal force - like force, but the force he is doing (exerting on the floor) is a push force, often called an applied force (a contact force) where he pushes the floor with his feet.

Answer:

The force Liam is doing (exerting on the chair) is a downward contact force (equal to his weight, a gravitational - derived force), specifically a type of normal force - like contact force (he pushes the chair down) or the force of his weight (gravity - related) acting on the chair.

Question 13