Forces in 2D and Circular Motion

Big Questions:

What does it mean to analyze forces in 2D?

• Forces analyzed in 2D have a length and a width
• 2D forces have an x as well as a y axis

How do forces cause objects to move in a circle?

• The center pointing (centripetal) forces make objects move in a circle. 
• When an object is moving in a circle, it is accelerating. The object is acceleration because acceleration = a change in velocity over a change in time. Velocity is a vector, and therefore changes. If velocity changes, the object accelerates.

This represents the equation for acceleration. 

• What does it mean to be in orbit? 
• When an object travels around another object as a result of the centripetal force. 

• How do satellites orbit planets? 
• Very similar to the way a plant is able to orbit the sun, satellites are able to orbit a planet. The speed of the satellite is adjusted when it orbits the planet so that it falls to earth at the same rate that the curve of the earth falls away from the satellite. 
• According to Newton's 1st law, there is an equal and opposite force for each force. The Earth pulls on the satellite and the satellite pulls on the Earth. Since there is no air resistance, the satellite continues falling into orbit around the earth.

• How do planets orbit the sun?
• The earth is able to rotate in orbit around the sun due the sun's centripetal force. However, even though the speed is constant, the direction is not. As a result the planets accelerate around the sun. The gravity of the sun acts as on the planets as the centripetal force that keeps them in orbit. Even though the planets and the sun's gravity both pull on each other, the planets orbit around the sun because it has more mass. The planets then fall around the sun because they are both curved.