Chapter 6 - Forces In Motion Section 2 – Newton’s Laws of Motion pp. 158 - 165

TERMS TO LEARN Inertia – the tendency of all objects to resist any change in motion Momentum – a property of a moving object that depends on the object’s mass and velocity.

NEWTON’S THREE LAWS OF MOTION In his book, Principia, Newton described the three laws of motion. He did not discover all three laws, he explained them in a way that many people could understand

NEWTON’S FIRST LAW OF MOTION This is also known as the Law of Inertia It says : An object in motion will remain in motion at a constant speed and in the same direction unless acted on by an unbalanced force. An object at rest will remain at rest unless acted upon by an unbalanced force.

NEWTON’S FIRST LAW OF MOTION In other words… Unless you apply a force, things tend to keep on doing what they were doing in the first place. Objects at rest (not moving) will not begin moving unless a push or pull is exerted on them.

NEWTON’S FIRST LAW OF MOTION

NEWTON’S FIRST LAW OF MOTION An object moving at a certain velocity will continue to move forever at that same speed and in the same direction unless an unbalanced force acts on it. Inertia is related to mass. Mass is a measure of inertia.

NEWTON’S FIRST LAW OF MOTION An object with a small mass has less inertia than an object with a large mass. For example… A tractor trailer has more mass than a motorcycle

NEWTON’S FIRST LAW OF MOTION How do ABS (automatic brake systems) work in cars? The system is controlled by a computer that prevents skidding by sensing when the wheels are about to lock.

ABS BRAKES EXPLAINED The computer releases and reapplies the brakes up to 25 times a second. Instead of skidding out of control, the car slows down and stops safely.

NEWTON’S SECOND LAW OF MOTION The acceleration of an object depends on the mass of the object and the amount of force applied to it. Equation: F = m∙a Force = mass times acceleration

NEWTON’S SECOND LAW OF MOTION Acceleration depends on force. Acceleration and force are directly proportional. This means as force increases acceleration also increases and vice versa.

NEWTON’S SECOND LAW OF MOTION Acceleration also depends on mass. Acceleration and mass are inversely proportional. This means as mass increases, acceleration decreases and vice versa. Remember that mass is also a measure of an object’s inertia. Complete Math Focus on p. 162 of text.

NEWTON’S SECOND LAW OF MOTION In other words… Force causes an object to accelerate, while the object’s mass resists the acceleration. The larger the object (the more mass it has), the harder it is to accelerate.

NEWTON’S THIRD LAW OF MOTION Whenever one object exerts a force on a second object, the second object exerts a force that is equal in size and opposite in direction on the first

NEWTON’S THIRD LAW OF MOTION In other words… For every action there is an equal and opposite reaction.

NEWTON’S THIRD LAW OF MOTION All forces act in pairs called action-reaction force pairs If a force is exerted, another force occurs that is equal in size and opposite in direction to the first. ACTION-REACTION FORCE PAIRS DO NOT ACT ON THE SAME OBJECT! See Figure 7 & Figure 8 on p. 164.

MOMENTUM Momentum is a property of a moving object that depends on its mass and velocity. The more momentum an object has, the harder it is to stop the object or change its direction.

MOMENTUM Equation for Momentum – p = m∙v Where p = momentum, m= mass and v = velocity