Acceleration & Force Section 8.2

Acceleration Acceleration = change in velocity divided by the time interval in which the change occurred. Equation: Acceleration = final velocity - initial velocity time a = ∆v m t s2 Unit=

Graphing Acceleration To graph acceleration: Plot velocity on the y - axis Plot time on the x - axis v v v t t t Traveling at constant velocity; a = 0 m/s2 a is increasing (+) a is decreasing (-)

Force When a force is exerted on an object it causes an acceleration, or change in an object’s velocity Usually a combination of forces act on an object at any given time (net force) An object accelerates in the direction of the net force.

Balanced/Unbalanced Forces Balanced forces: forces cancel each other out. Net force= zero so there is NO movement. Unbalanced forces: forces acting on an object produce a nonzero net force Acceleration of an object is in the direction of the greater force. Therefore movement occurs.

Here is an example of balanced forces Here is an example of balanced forces. There is no movement by either object. Figures a, b, and c are all examples of unbalanced forces because there is change in motion.

Friction The force between two objects in contact that opposes the motion of either object. Frictional force will vary according to surfaces rough - rough smooth – smooth  frictional  frictional force forces

Air Resistance Form of friction… Air resistance = the interaction between surface of an object in motion and air molecules. Depends on size, shape, and speed of the object. Lots of air resistance Not a lot of air resistance (aerodynamic)

Gravity defined as the attraction between two particles of matter due to their mass Gravity occurs between all objects Acts on objects even when they do not touch Depends upon mass and distance  mass,  force of  distance,  force of gravity gravity

Look mom, no gravity!

Now I’m Freeeeee, Free Falling… -Tom Petty Free Fall = the motion of a body when only the force of gravity is acting on it free fall acceleration = g (force of gravity) g = 9.8 m/s2 near earth’s surface Weight = force on an object due to gravity w = mg where g is equal to 9.8 m/s2 Weight is a force so its unit is N

Relationship between velocity/ air resistance/weight When the force of air resistance becomes equal to the gravitational force on an object, the object stops accelerating & reaches maximum velocity or terminal velocity.

Notice, as the weight of the person increases so does the air resistance and the force of gravity on that person’s mass