Chapter 4 Forces

What is a force? Push or a pull Can push or pull by with or without touching Field forces: no contact required Contact forces: objects must touch to push or pull Vectors, forces have both magnitude and direction Forces can cause acceleration Acceleration is change in Direction Magnitude SI units for force: newtons, N or kg m/s2

force demonstration

Newton’s Laws of Motion Newton’s first law Inertia Objects remain at rest or move at constant velocity unless acted upon by a net, unbalanced force Use free body diagrams to determine if there is a net force. Free body diagram Illustrates all the forces that are acting upon an object Show relative size and direction of each force

Newton’s Laws of Motion Newton’s Second Law Acceleration The acceleration of an object is directly proportional to the net force on the object and inversely proportional to the mass of the object Net F = m a acceleration demonstration

Newton’s Laws of Motion Newton’s 3rd Law Action-reaction

Newton’s Laws of Motion Newton’s 3rd Law Action-reaction When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body. Fof 1 on 2 = -Fof 2 on 1 Action-reaction demonstration

Newton’s Laws of Motion Newton’s 3rd Law Fof 1 on 2 = -Fof 2 on 1 more action-reaction