Reading Questions for Holt Physics Chapter 4

Determine from the reading whether the following statements are True, False, or there is not enough information in the text to know (NEI).

  1. Force is a scalar quantity.
  2. For a force to be exerted two objects must be in contact with one another.
  1. When you draw an arrow representing a force in an FBD, it is important to label the arrow with either the magnitude of the force or a name that will distinguish it from the forces acting on the object. Also be sure that the length of the arrow approximately represents the magnitude of the force.
  2. The FBD of a sled will show all the forces acting on the sled as if the forces are acting on the center of the sled. First, draw and label an arrow that represents the force exerted by the string attached to the sed. The arrow should pint in the same direction as the force the sting exerts on the sled.
  3. When dealing with forces it is often important to deal with the total force. This is often referred to as the Net force. The Net Force is the Vector sum of all the external forces acting on an object.
  4. When the Vector sum of all forces equals zero the object is said to be in equilibrium. In equilibrium Fnet=0. If Fnet=0 then the object is either moving at constant velocity or at rest.
  5. According to Newton’s third law there are action reaction pairs. However this means that the equal and opposite forces balance one another and make any change is the state of motion impossible.
  6. Even field forces such as gravity act in pairs. If you drop the head of a crash test dummy it accelerates towards the floor. At the same time the earth accelerates towards the dummy’s head. However this goes against our everyday experience because the earth is so massive that its acceleration is negligible (too small for us to notice).
  7. When an object has weight but is at rest (a=0, v=0) their must be a balanced forces keeping it in equilibrium. Often this balancing force comes from a force perpendicular to the surface of contact. This force is called the Normal Force.
  8. When you try to push an object at rest you are resisted by static friction. This force opposes your force and increases equally with the force applied until it reaches some maximum value Fmax. After Fmax is reached the object will start to slide and the friction will change from static friction to kinetic friction.
  9. The force created by kinetic friction is always greater than the force of static friction. This is due to the fact that as the normal force increases the force of friction decreases.
  10. To find the force of friction we must use the coefficient of friction μ. The coefficient of friction is found by experiment and a list of values is found on page 138.
  11. Although we usually ignore it due to its complicated nature Air resistance is simple a force of friction created by an object rubbing against air molecules. Air resistance is complicated because it increases as speed increases. Often during free fall it increases until it is equal to the falling objects weight. When the air resistance equals the weight the object is in equilibrium (Fnet=0) and the object has reached terminal velocity.