Forces Notes #4 Newton’s Laws

Sir Isaac Newton Sir Isaac Newton was one of the greatest scientists and mathematicians that ever lived. He was born in England on December 25, 1643.

Sir Isaac Newton While Newton was in college he was writing his ideas in a journal. Newton had new ideas about motion, which he called his three laws of motion. He also had ideas about gravity, the diffraction of light, and forces. Newton's ideas were so good that Queen Anne knighted him in 1705. His accomplishments laid the foundations for modern science and revolutionized the world. Sir Isaac Newton died in 1727.

Newton’s 1st Law Objects at rest stay at rest Objects in motion stay in motion Unless acted upon by an unbalanced force

1st Law: Law of Inertia What does it mean? This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

What does Newton’s 1st Law of Motion say? All objects have inertia (the tendency to resist changes in motion). An object will only change its motion if unbalanced forces act on it.

What is Inertia? Tendency for an object to resist a change in motion.

What is Inertia? Objects with more mass have more inertia which means it is harder to change their velocity. Objects with less mass have less inertia so it is easier to change their velocity.

OUTSIDE FORCE

Which has more inertia?

Which has more inertia?

MORE MASS>>>>MORE INERTIA! Which has more inertia? A 5 kg ball with a volume of 5 cm3 A 10 kg ball with a volume of 1 cm3 MORE MASS>>>>MORE INERTIA!

What happens to an object if balanced forces are exerted on it? The object’s velocity will not change. The object is either not moving or moving in a straight line at constant speed. Net force = 0

What happens to an object if unbalanced forces are exerted on it? The object’s velocity will change. It will speed up, slow down, or change direction. Net force = not 0

Newton’s 2nd Law The rate of change of momentum of an object is directly proportional to the resultant force acting on it…. Force = mass x acceleration

2nd Law: F = ma What does it mean? Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

What does Newton’s 2nd Law of Motion say? The force an object can exert depends on the object’s mass and acceleration.

How do I calculate Force? Force = F Acceleration = a Mass = m F m a

What is the equation for force? Force = mass x acceleration

What happens to the force of an object if you double the mass? When you double an object’s mass, you double the force it can exert. F = ma F = ma F = (2 kg)(10 m/s2) F = (4 kg) (10m/s2) F = 20 N F = 40 N

What happens to the force an object can exert if you double its acceleration? When you double an object’s acceleration, you double the force it can exert. F = ma F = ma F = (10 kg)(5 m/s2) F = (10 kg) (10m/s2) F = 50 N F = 100 N

How would doubling the size if the unbalanced force affect the acceleration of the object? a) If you double the size of the force you will double the acceleration. b) If you double the mass of the object, the acceleration will decrease if the same force is exerted. How would doubling the mass of the object being pushed affect the acceleration of the object?

Which will exert more force if it hit your toe? Bowling Ball Ping pong ball

Which will exert more force to accelerate? Empty cart Cart with groceries in it

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

3rd Law: Action/Reaction What does it mean? For every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

What does Newton’s 3rd Law of Motion say? The forces are equal and opposite. Forces come in pairs

Practice:

1. F = ma F = 6-3 = 3 m = 100 kg a = ? 3 N = 100kg x a 3N = a 100kg a = .03 m/s2 Note: N = kg x m s2