Introduction to Forces

What is a force? Force: Any push or pull. The units of force are Newtons (N) There are four fundamental forces that make up all of the forces in the universe: 1) Gravitational Force 2) Electromagnetic force 3) Strong Nuclear Force 4) Weak Nuclear Force

Gravitational Forces Force of attraction between all objects as a result of their masses and distances between them. The higher the masses and the shorter the distances between two objects, the greater the force of gravity. The smaller the masses and the larger the distances between two objects, the weaker the force of gravity.

Gravity exists between ANY two objects

Electromagnetic Force Force of attraction or repulsion between two charged objects or between the poles of two magnets We already discussed this at the beginning of the year Likes repel, opposites attract

Strong and Weak Nuclear Forces Act within the nucleus of an atom Short range forces Holds the nucleus together

Contact Force vs Field Force Contact Forces Field Forces Frictional Force Gravitational Force Tension Force Electrical Force Normal Force Magnetic Force Air Resistance Force   Applied Force Spring Force

Definitions Force of Gravity: Any two objects will feel a force of attraction that depends on their masses and distance apart. Mass (kg): The amount of matter in an object. Weight (N): The amount of gravitational force felt by an object. Mass is constant throughout the universe whereas weight changes depending on where you are.

Formula for force Fg = mg The formula for force of gravity is: Where: Fg = Force of gravity m = mass (kg) g = acceleration due to gravity (m/s2) = gravitational field strength

Gravitational Field g varies depending on Mass of the planet Distance to the planet For example On earth g = 9.8 m/s2 On the moon g = 1.6 m/s2 On Jupiter g = 24.5 m/s2 On the sun g = 274 m/s2 Notice that the acceleration due to gravity values are NOT NEGATIVE!

Determine your weight Determine your weight (in Newton’s) on: a) Earth b) The Moon c) Jupiter

G-forces G-Forces are actually a measurement of acceleration experienced by an object. It is related to the supporting reaction force that an object experiences due to acceleration. While at rest on Earth you are experiencing 1g Thus on Earth 1g = 9.8 m/s2

Find the g’s please 1) A car accelerates at 4.9 m/s2, what is the g-force? Answer – (4.9 m/s2)(1 g/9.8 m/s2) = .5 g 2) During lift-off a shuttle will accelerate at 28 m/s2. How many g-forces do the astronauts feel? Answer – (28 m/s2)(1 g/9.8 m/s2) = 2.9 g 3) A normal human can withstand 4.0 g’s, while a pilot can withstand 9 g’s. What is the acceleration of each? Answer – (4 g)(9.8 m/s2/ 1g) = 39.2 m/s2 Answer – (9 g)(9.8 m/s2/ 1g) = 88.2 m/s2