Newton’s Second Law of Motion Force & Acceleration

1. Newton’s Second Law of MotionForce & Acceleration Introduction to Science A. King EHS

2. Acceleration • Galileo define rate of change of velocity as acceleration. • The term acceleration is typically used when the velocity increases. • The term deceleration is typically used when the velocity decreases – another way of saying this is that “deceleration” is when negative acceleration is occurring. • In both cases, “acceleration” is the process that’s actually occurring.

3. ΔV Acceleration = --------- t Where ΔV is the change in velocity and t is the time it takes for the velocity to change. ΔV : : x t acc Calculating Acceleration

4. Speed and velocity are easily measured in distance/time units, such as miles/hr, m/s, etc. Units of acceleration are more complicated, and have to take other stuff into account. Sample problem: What is the acceleration if we speed up from 10 km/h to 30 km/h in 10 seconds? Acceleration = Δv/t (30 km/h – 10 km/h)/ 10 sec = 2 km/h/s Units for Acceleration

5. Acceleration depends on the net force. Acceleration ~ net force.

6. Mass • Mass is a measure of an object’s inertia and a measure of how much material an object contains. (It depends on the number and kind of atoms making the object up.) • Mass is measured in grams: grams, kilograms, milligrams…

7. Weight • Weight depends on gravity. • Weight is the force due to gravity that acts on an object’s mass. • Although weight and mass are different from each other, they are directly proportional to each other. • 1 kilogram weighs 9.8 newtons.

8. Volume • Volume is a measure of space.

9. Newton’s Second Law states: • The acceleration produced by a net force on an object • is directly to the net force. • Is in the same direction as the net force. • Is inversely proportional to the mass of the object. • In formula: F = m x a

10. By using consistent units, such as newtons (N) for force, kilograms (kg) for mass, and meters per second squared (m/s2) for acceleration, we get the exact equation: Δ v vf – vi Acceleration = -------- = ---------- t t

11. Acceleration Problems • While drag racing out of our school parking lot, I time myself at a speed of 40 meters per second seven seconds after starting. What was my acceleration during this time? • A = vf – vi / t • = (40 m/s – 0 m/s )/7s • = (40 m/s)/7s • = 5.7 m/s/s

12. Friction • Occurs when one object rubs against something else. • Occurs for solids, liquids and gases. • Always acts in a direction opposite to motion. • The amount of friction between two surfaces depends on the kinds of material and how much they are pressed together.

13. Free Fall • When an object is dropped in a place with gravity (k.e. not deepspace), gravity causes the object to fall downward. • When this occurs, the object is said to be in “free fall.” • For problems like this, we’ll imagine that gravity is the only force that’s acting on the object – wind resistance and other stuff will be ignored.

14. Let’s consider the following data table: The increase in speed per second is the acceleration which in this case is 10 m/s/s. The instantaneous speed of an object that is accelerating is equal to the acceleration multiplied by the amount of time the object is falling. In equation form: v = at How fast is an object moving in free fall?

15. F v : : : : t a m a x x Formulas Δv acceleration vf - vi acceleration : : : : x x t t acc acc Newton's 2nd Law freefall distance weight instantaneous speed d Wt : : : : g m x x t2 ½ g