3 - FORCE, WORK, ENERGY, POWER

• What branch of physics deals with forces and motion?

  Mechanics
• What are the two main parts of mechanics?

  • Kinematics: Describes motion without forces
  • Dynamics: Effects of forces on motion
• Who formulated the first concepts of mechanics?

  Isaac Newton
• When were Newton's major works on mechanics published?

  1687
• Who conducted early studies on mechanics in the 4th century B.C.?

  Greek Philosophers like Aristotle
• What did Leonardo da Vinci study related to mechanics?

  Animal motions and muscle functions
• How have studies in mechanics been aided?

  • Analytic techniques
  • Development of instruments (e.g., cameras, timers)
• What does kinesiology study?

  Human motion in athletic activities
• What is biomechanics concerned with?

  Muscle movement and physical behavior of organs
• What is the definition of force?

  • A push or pull on a body
  • Tends to change the state of motion
• What is the formula for force?

  $F =$$ma$
• What does it mean when the sum of all forces is zero?

  The body is in translational equilibrium
• What is torque?

  The tendency of a force to rotate an object
• What is the formula for torque?

  $\tau =$$r \times F$
• What does it mean when the sum of all torques is zero?

  The body is in rotational equilibrium
• What is static equilibrium?

  • Vector sum of forces is zero
  • Vector sum of torques is zero
• How does Earth affect an object's weight?

  It exerts an attractive force on the mass
• What is the center of mass?

  The point where weight acts on a body
• What is required for a body to be in stable equilibrium?

  • Proper support
  • Center of mass over the base
• What happens if the center of mass is outside the base?

  The body will topple due to torque
• How does the width of the base affect stability?

  • Wider base increases stability
  • Narrow base decreases stability
• What happens when the center of mass is closer to the base?

  The body is more stable
• Where is the center of gravity for an erect person?

  Approximately 56% of height from feet
• What happens to the center of gravity when a person moves?

  It shifts when the person bends or moves
• How can a person maintain balance when carrying an uneven load?

  By shifting the center of gravity over the feet
• How does spreading legs increase stability?

  It lowers the center of gravity
• What can happen to a person who has lost an arm?

  Permanent distortion of the spine may occur
• What external forces can affect the stability of the human body?

  • Downward force of weight
  • Other applied forces
• What happens to a person in stable equilibrium without external forces?

  The center of mass is above the feet
• What is the pivot point when toppling occurs?

  Point A, where the body pivots
• What is the direction of torque?

  It can be counterclockwise or clockwise
• What is the formula for counterclockwise torque?

  $\tau_a =$$F_a \times 1.5m$
• What is the formula for clockwise torque?

  $\tau_W =$$W \times 0.1m$
• What happens when the two torques are equal?

  The person is on the verge of toppling
• What is the maximum applied force to prevent toppling?

  $F_a =$$W \times 0.0667$
• How does bending away from a force help stability?

  • Shifts center of gravity
  • Increases lever arm of weight
• What is the minimum pushing force for a 60.0 kg person to start toppling?

  50.4 N
• What is the weight of a 60.0 kg person?

  $588 N$
• What is the lever arm of the applied force for the person?

  $1.40 m$
• What is the lever arm of the weight for the person?

  $0.120 m$