Force and Acceleration
Newton's Second Law of Motion
- I can interpret and construct a force (free-body) diagram.
- I can diagram and calculate the components of force acting in two dimensions.
- I can describe the relationship between net force, mass, and acceleration.
- I can calculate the net force, mass, or acceleration of an object.
- I can explain the difference between mass and weight given a changing gravitational field.
- I can calculate apparent weight given a situation of vertical acceleration.
- I can evaluate and develop a mathematical model for elastic (spring) forces.
- I can predict the force required to slide an object relating to the coefficient of friction.
- I can predict an object's motion and the associated forces of objects moving in a circle.
- Fnet = m a
- a = Δv / Δt
- Δx= ½ at2 (if v0 = 0)
- v12 = v02 + 2a (Δx)
- Felastic = k Δx
- Fk = μkFN
- ac = v2 / r
- Fc = mv2 / r
- circular-have the form of a circle
- centripetal-a force that acts on a body moving in a circular path and is directed towards the center around which the body is moving.
- centrifugal-moving or tending to move toward a center
- free-body diagram-diagrams used to show the relative magnitude and direction of all forces acting upon object in a given situation.
- friction-the resistance that one surface or object encounters when moving over another.
- kinetic-of, relating to, or resulting from motion
- static-lacking in movement, action, or change, especially in a way viewed as undesirable or uninteresting
- linear-arranged in or extending along a straight or nearly straight line
- normal force-the component, perpendicular to the surface of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall, preventing the object from falling
- net force-the overall force acting on an object
- tangent-a straight line or plane that touches a curve or curved surface at a point, but if extended does not cross it at that point
- torque-a twisting force that tends to cause rotation
- weight-a relative mass or the quantity of matter contained by it, giving rise to a downward force
- apparent-clearly visible or understood, obvious
- weightlessness-having little weight or lacking apparent gravitational pull
Practice Problem #1
What is the estimated acceleration due to the gravitational force on the moon if a person on Earth weighs 550 N- but only 75 N on the Moon?
Practice Problem #2
A rider on a motorcycle with a combined mass of 300 kg are going down the road at 40 m/s. The rider wants to stop and applies the brakes until coming to rest. What force will the brakes need to apply in order for the rider to stop in a distance of 150 m?
Practice Problem #3
Suppose a net force of 34 N is applied horizontally while pushing a desk weighing 545 N. Assuming there is no friction, what is the displacement of the desk after 10 seconds?
This unit covers:
- problems involving gravitational forces, elastic forces, and frictional forces.
- calculating the weight using force diagrams and Newton's laws of motion.
- the difference between mass and weight.
- kinetic and friction forces
- net forces acting in two dimensions with vector addition trigonometry or diagrams.
- solving for net force, final velocity, time , displacement, and acceleration for objects sliding down different types of inclines.
- calculating centripetal force by using a separate equation.