What Happens When Forces Act on Objects? Lesson 1

Forces A force is a push or a pull A force has both size and direction Some forces act only if the two objects touch; i.e. elephant on a ball Other forces act even when the objects do not touch; i.e. Earth’s gravity on you or magnets repelling each other

Measuring Forces Force is measured with a spring scale Spring stretches if the force is greater Unit of measurement is a Newton Newton is defined as the amount of force needed to change the speed of a 1 kilogram object one meter per second per second

Forces on an Object If forces are balanced, the object does not move If the forces are unbalanced, the object changes speed and/or direction Net force is the sum of all forces working on an object 5 N force to the right and a 3N force to the left, overall force is 2 N to the right

Friction Friction is a force that resists the movement of one surface past another Rough surfaces tend to create more friction than smooth surfaces Rolling friction – resists the motion of a rolling object Sliding friction – resists the motion of a sliding object Static friction – resists the motion of an object just as it begins to move

Helpful and Harmful Friction Helpful friction allows you to walk across the room without slipping Friction on a brake to help you slow down Harmful friction – Friction in a car engine can be harmful to metal engine parts if the rub against each other Friction causes soil erosion and weathering Wears away tires, soles of shoes

How does gravity affect objects? Lesson 2

Gravitational Forces Gravitational force is a force of attraction between any two objects First explained by Newton in 17th century Depends on two things – mass and proximity (how close) Weight is the force of gravity pulling on you, less on the moon because the force of gravity is less

Gravity and the Universe Gravity determine the motion of the planets and stars The Sun is the most massive object in our universe, thus everything revolves around it We don’t feel the gravitational pull of the Sun because we are not as close to it as we are to the Earth’s core

Tides A tide is the rise and fall in water level near the ocean shore Moon’s gravitational pull has more of an affect on liquids than solids The Moon’s gravity causes the tides in Earth’s oceans We have two high tides each day because the water is being pulled away from the Earth; he other high tide is when the water gets pulled away on the opposite side