Force • A push or pull on an object. • Described by: • A force gives an object energy to: • STRENGTH • DIRECTION • STOP MOVING • START MOVING • CHANGE DIRECTION
Types of Force • Contact Force • Non Contact Force
Contact Force • A push or pull on one object by another that is touching it. • Contact forces can be: • Strong • OR • Weak
Noncontact Force • A force that one object can apply to another object without touching it. • Examples Include: • Gravity • Magnetic Force • Electric Force
Strength and Direction of Forces • can be used to show forces. • The of an arrow shows the of the force. • The that the arrow points shows the direction in which the • The stronger the force the the arrow. ARROWS LENGTH STRENGTH DIRECTION FORCE WAS APPLIED LONGER
Strength and Direction of Forces NEWTON • The SI unit for force is the • The symbol for Newton is • One Newton = about the force you exert to lift a lime. • Named after: N Sir Isaac Newton (founder of physics)
Gravity • An attractive force that exists between all objects that have mass. Force of gravity • On EARTH the force of gravity = 9.8 m/s2 • All objects fall to the Earth at an acceleration of 9.8m/s2 due to the force of gravity.
The Law of Universal Gravitation • Sir Isaac Newton (1600’s) • The law states: • Factors Affecting Gravity • All objects are attracted to each other by a gravitational force. The strength of force depends on the MASS of each object and the DISTANCE between them. • MASS • DISTANCE
Mass • The amount of matter in an object. Which object has more mass? Which object has more mass?
Gravitational Force and MASS INCREASES • When the mass of one or both objects the gravitational force between them also • Regardless of the amount of mass an object has the will be the • Each object exerts the attraction on the other object. INCREASES FORCE ARROWS SAME SIZE SAME
Gravitational force and DISTANCE • The attraction between objects as the between the object DECREASES INCREASES DISTANCE
Weight • The gravitational force exerted on an object. • Weight is measured in • Near Earth’s surface the object’s weight is the NEWTONS FORCE DUE TO GRAVITY
Weight and Mass on Earth • Weight and mass are related, but ARE NOT the same. • Weight can due to • Mass change FORCE = GRAVITY CHANGE DOES NOT MASS x ACCELERATION F = Weight on Earth = M x A MASS x 9.8m/s2 (acceleration due to the force of gravity)
Examples: • What would an object with a mass of 10 kg weigh? • If your mass was 50kg, what would your weight be?
Net Force • The combination of all the forces acting on an object. • To calculate the net force: • If the forces act in the same direction they are added together. • If forces act in opposite directions they are subtracted.
Combining Forces - Unbalanced • Forces acting on an object that combine and form a net force that is not zero. • Unbalanced forces cause an object to move. • Forces moving in the same direction are • Forces moving in the opposite direction are ADDED SUBTRACTED
Combining Forces – Balanced Forces • Forces acting on an object that combine and form a net force of ZERO. NO change in motion.
Friction • A force that resists the motion of two surfaces that are touching. • Types of friction • STATIC FRICTION • SLIDING FRICTION • FLUID FRICTION
Static Friction • Friction that acts on objects that are not moving.
Sliding Friction • When solid objects slide over each other.
Fluid Friction • A force produced by a fluid (gases or liquids) Examples: engine oil, grease • Air resistance • Air resistance is affected by: *objects with more surface area have more air resistance** • a type of fluid friction • Upward force exerted on falling objects. • SHAPE • SIZE • MASS
What causes friction? 2 causes of friction • Surface roughness • Attraction between particles (positive and negative)