# Unit 4 Forces and Acceleration

### Newtons 2nd law

## I can statements

I can diagram and calculate the components of force acting in two directions.

acting in two different directions.

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 situation of vertical acceleration.

I can evaluate and develop a mathematical model for elastic 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.

## Formulas

Felastic = k Δx Fk = μkFN ac = v2 / r Fc = mv2 / r

Fnet – net force (Newtons) m – mass (kg) a – acceleration ag or g = 9.8 m/s2 on Earth – assumed Fg = mg or [W for weight] k – spring constant (N/kg) Δx – change in position (m) μk – coefficient of kinetic friction FN – normal force (N) r – radius (meters)

## Vocabulary

Centripetel- Trending towards a center.

Centrifugal- Outward force apparent in a rotating reference frame.

Free-body diagram- Diagrams used to show relative magnitude and direction of all forces.

Friction- The force resisting the relative motion of solid surfaces.

Kinetic- A friction created by moving or sliding action.

Static- A friction between a stationary object and the object it is resting on.

Linear- Moving in a straight line.

Normal force- The component, perpendicular to the surface of contact.

Net force- The total of forces acting on an object.

Tangent- The straight line that just touches a curve at one point.

Torque- Force used to turn or rotate an object.

Weight- Measured by multiplying your mass and the gravity. (9.8 m/s on Earth)

Apparent- Clearly understood or obvious.

Weightlessness- Two bodies accelerating at the same speed making you feels as if you do not weigh anything lacking gravitational pull.

## Practice Problems

## Main points

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

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.