Lesson: Forces that Resist Motion Physics

Students will be able to

• recognize that frictional forces can act between surfaces that are in contact,
• recognize that frictional forces act in the opposite direction to the motion of a moving object,
• recognize that frictional forces can act on a stationary object that is in contact with a surface,
• recognize that frictional forces acting on a stationary object on a surface occur only if some force acts on the object that would make the object move along the surface if no friction existed,
• recognize that frictional forces acting on a stationary object on a surface act in the opposite direction to forces that would make the object move along the surface if no friction existed,
• recognize that the motion of an object within a fluid produces a force on the object in the opposite direction to the motion of the object called drag force,
• recognize that the magnitude of the drag force on an object is related to the mass of fluid displaced by the object per unit time and hence increases when an object’s velocity within a fluid increases,
• recognize that the magnitude of the drag force on an object can equal the magnitude of the forces that accelerate the object to move within the fluid and that when this occurs the object moves at a constant velocity called terminal velocity,
• qualitatively describe how the shape of an object affects the drag force acting on it.