Forces Def – an action exerted on an object to change the object’s state of motion (resting or moving) – Magnitude and direction – Units: Newtons (N) Net force – total force on an object – When there is a net force on an object, the object accelerates in the direction of the net force – If net force = 0, then the object does not move

Balanced forces Net force = 0, no movement – Forces are balanced – An object standing still will not move – An object moving will not stop

Unbalanced Forces Net force is greater than zero, unbalanced force – Object will move

Friction Force that opposes motion between two surfaces that are in contact 2 types – Static – friction between two forces at rest, initial friction an object must overcome – Kinetic – friction between two moving objects Static friction is usually greater

Newton’s Laws He was born the same year that Galileo died Newton had ideas about motion, which he called his three laws of motion – Also had ideas about gravity, the diffraction of light, and forces Physics and Math Helped create Calculus

First Law Law of inertia – An object at rest will stay at rest and an object in motion stays in motion unless acted on by an external force Inertia – tendency of an object to stay at rest or stay in motion – Mass is a measure of inertia – Small mass = less inertia Seatbelts

Second Law The unbalanced force acting on an object equals the object’s mass times its acceleration – F=ma – Force is measured in Newtons (N) 1 N = 1 kg x 1 m/s 2 Q: What is the force necessary for a 1600 kg car to accelerate forward at 2.0 m/s 2 ?

2 nd Law Problem Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s 2. Using Newton's Second Law, compute how much force Mike is applying to the car.

Third Law For every action there is an equal and opposite reaction – Opposite in direction. – Whenever an object pushes another object it gets pushed back in the opposite direction equally hard Example: Balloon full of air being released

Force of Gravity All objects in the universe attract each other through gravitational force Mass increases – force of gravity increases Distance increases – force of gravity decreases

Force of Gravity Free fall – only force of gravity is affecting an object Calculate the acceleration at which an object free falls – Earth – 9.8 m/s 2

Force of Gravity Weight is not the same as mass – Depends on gravity – Different locations have different gravities and therefore different weights Force of gravity on an object is weight – w=mg – Newtons (N)