Newton’s Laws of motion Explains the natural laws that govern the motion of objects. There are 3 of them!!!

Newton’s 1st Law of Motion Object in motion stays in motion

Newton’s 1st Law of Motion And Objects at rest stay at rest

Newton’s 1st Law of Motion Until they are acted upon by unbalanced forces.

Inertia or Newtons 1st Law Tendency for an object to stay at rest or moving in a straight line at a constant speed. The mass (m measured in kg) of an object determines its inertia(more mass more inertia) Inertia comes from the Latin word meaning lazy.

Examples from Real Life A powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them. On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).

Newton’s 2nd Law of Motion Force = Mass X Acceleration F=ma The force exerted by an object is related to its mass and its acceleration. Larger and faster objects exert more force.

Newton’s 2nd Law of Motion The greater the mass of an object, the greater the force required to change its motion.

Newton’s 2nd Law of Motion The greater the acceleration of an object, the greater the force required to change its motion.

What does F = ma mean? Force is directly proportional to mass and acceleration. Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain amount of force. Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

Real Life examples of F = ma

Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2. The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping? Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2. So, .5 kg x 3 m/s2= 1.5 N

Newton’s 3rd Law of Motion For every action force there is an equal and opposite reaction force.

What does this mean? For every force acting on an object, there is an equal force acting in the opposite direction. These forces are not acting on the same object so the forces are not balanced and changes in motion occur. Ex. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish . For every action, there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

Think about it . . . What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

Newton’s 3rd Law of Motion All forces come in action-reaction pairs Ex: feet push backward on floor is the action force, the floor pushes forward on feet is the reaction force. The ball pushes down on the ground is the action force The floor pushing up on the ball is the reaction force.