4.2 Newton’s Laws of Motion

Sir Isaac Newton (1642-1727) Discovered laws of motion and gravity

Newton's Laws of Motion First Law: An object at rest stays at rest and an object in motion, stays in motion (same direction & same speed) unless acted upon by an unbalanced force Also called the Law of inertia

Inertia is a property of matter that causes it to resist any change in its motion more mass = more the inertia more speed = more the inertia

What is a Force? FORCE = Any push or pull acting on an object Force is measured in Newtons.

Newton's Laws of Motion Second Law: The acceleration of an object is proportional to the net outside force acting on the object Force = mass object  acceleration of object Formula: F = ma

Forces can be BALANCED or UNBALANCED Balanced forces are equal in size and opposite in direction Unbalanced forces are not equal in size and/or opposite in direction. If the forces on an object are unbalanced, we say there is a NET force.

The greater the force, the greater the acceleration The greater the mass, the greater the force needed for the same acceleration

Examples of Newton’s 2nd Law Bunting the baseball, versus a grand slam The positioning of football players - massive players on the line, lighter (faster to accelerate) players in the backfield Pushing a loaded versus an unloaded truck

Newton's Laws of Motion Third Law: For every force, there is always an equal and opposite reaction force.

Example of Newton’s 3rd Law

Weight: a measure of the gravitational force between two objects Weight = (mass) x (acceleration due to gravity) Formula: W = mg more mass = more weight

How is mass different from weight? Mass – the amount of matter in an object Weight – the force that acts on the object

Weightlessness – free from the effects of gravity?

There is gravity in space Weightlessness is due to a constant state of free-fall