Worksheets due Dec 15, 2022 10:00 PST Completed Forces exerted by ideal springs are described by Hooke's law: Fs =- kx where k is the spring constant and 2 the displacement. In the case of springs, the displacement is the amount of stretch or compression from equilibrium (when no force is applied to the spring). WQ5.4 1/1 point (graded) 3 Compressed 0 Before After A 1.5 kg block is put on top of a 60 cm long strong, which is then compressed to a new length of 35 cm. What is the spring constant k? Give your answer is units of [N/m]. 60 V 60 The word normal means that this is a force that is directed perpendicular ('normal') for a surface. In most cases this is a type of an elastic force (like a spring force) that is exerted by solid surfaces. The elasticity is due to molecular bonds that are compressed like springs. You already know that normal forces support objects against the fore of gravity (book on a table, person standing on a floor), but normal forces can be exerted by any surface, so they don't have to be vertical forces. Key is here that there are two surfaces in constant: PHYSICS The compressed molecular springs push opwand on the object. Molecular bonds The cover of the book is in contant with the table. Your feet are in contact with the floor. If you push a box, the box exerts a normal force on your hand. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force back on the first. If you push against a wall, you feel the wall exert force back on your hand. The force arises because the wall have some elasticity (a spring-like force). All forces come in pairs. It is sometimes difficult to identify interacting forces. These rules will help you: 1. Each force is a member of a pair of forces, often called action/reaction, that interacting objects exert on each other. 2. Each member of the action/reaction pair acts on a different object, i.e. the two forces are never exerted on the same object. 3. The forces of an interaction pair are equal în magnitude, but opposite in direction. 4. The interacting forces are of the same kind. All four rules must be satisfied. It helps to look at a few examples to see what these rules mean.
WQ5.5 2/2 points (graded) Forces need an 'agent'. This could be a person or an object that exerts the force on another object. a) What is the agent of the force that is pulling the box toward the ground? gravity v b) According to Newton's third law, the box should exert a force as well. On which object does the box exert an equal and opposite force? the earth V