Reaction

 “For every action, there is an equal and opposite reaction.”  This means that for every force that is exerted by one body on another, there is an equal and opposite force exerted by the second body on the first.  Some of the results of this law are: ◦ A force acting anywhere always has a force equal to that acting in the opposite direction ◦ Forces work in pairs opposing one another. ◦ The initial force (action force) is opposed by a second force (reactive force)  For example, if a sprinter pushes back on their starting block when the gun goes off, the block will push back on the sprinter’s foot and propel them in the opposite direction (forward). What is happening when two people push against each other forcefully, yet neither moves?

  mRU mRU

 nDnKU nDnKU

You have just identified Newton’s Three Laws of Motion.  Classify the following examples as either ◦ LAW of Inertia ◦ LAW of Acceleration ◦ LAW of Reaction LAWEXAMPLES A book lying on a desk, a body lying on the ground. In both these cases the action force - weight of the book and body is balanced by the reaction force - ie. support provided by the table and ground. The greater the mass of the ball struck by a force the greater the velocity (up to a point). eg. compare the distance a baseball travels to that of a softball. A shot put (3kg) will lie on the ground until a force of greater than 3kg picks it up. The greater the force applied the greater the change in speed (velocity) of the moving object. eg. - the faster the bat is swung the faster the ball will travel when hit. A softball hit at 45 0 into the air will continue to travel at that angle until the air resistance slows it down causing it to fall back to earth. Now moving situations: an athlete running a hundred metre race. Each stride he takes he applies an action force, that of the ground supporting his big drive is equal therefore he is able to move. Reaction Acceleration Reaction Acceleration Inertia Reaction