Forces Unit Note-Taking

What is a force? 1. In science, a force is a push or a pull. 2. When one object pushes or pulls another object, the first object is exerting a force on the second object.

3. The SI unit used to measure the strength of a force is the newton.

Combining Forces 1. The overall force on an object after all the forces are added together is called the net force. 2. When two forces act in the same direction, they are added together.

3. Unbalanced forces can cause an object to do three things. They are: a. Start moving b. Stop moving c. Change direction

4. Equal forces acting on one object in opposite directions are called balanced forces. 5. When you add equal forces exerted in opposite directions, the net force is zero.

Friction 1. When two surfaces rub, the irregularities of one surface get caught on those of the other surface. 2. Friction acts in a direction opposite to the object’s direction of motion.

3. The strength of the force of friction depends on: a. The types of surfaces involved b. how hard the surfaces push together

4. Why does some friction occur with seemingly smooth surfaces? Even surfaces that seem smooth have irregular bumps that can be seen with a microscope.

5. When an object moves through a liquid or gas, it is called fluid friction. 6. When solid surfaces slide over each other, it is called sliding friction.

7. Rolling friction is when an object rolls over a surface. 8. When objects are not moving, we call this static friction.

Gravity 1. The force that pulls objects toward each other is called gravity. 2. The universal law of gravitation states: The force of gravity acts between all objects in the universe.

3. The force of attraction between two objects varies with two factors: a. mass b. distance between the objects

4. How is weight different from mass? Weight is a measure of the force of gravity on an object, while mass is a measure of the amount of matter in an object. 5. Weight is usually measure in newtons.

Gravity and Motion 1. An object is said to be in free fall when the only force acting on the falling object is gravity. 2. Objects falling through air experience a type of fluid friction called air resistance.

3. The greatest velocity a falling object reaches is called terminal velocity. 4. The greater the surface area of an object, the greater the air resistance. 5. An object that is thrown is called a(n) projectile.

The First Law of Motion 1. Newton’s first law of motion states: An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity unless it is acted upon by an unbalanced force.

2. Another name for Newton’s first law is the law of inertia. 3. The amount of inertia an object has depends on its mass.

The Second Law of Motion 1. Newton’s second law of motion states: Acceleration depend on the object’s mass and on the net force acting on the object.

2. The equation that describes the relationship among the quantities of force, mass, and acceleration is: Acceleration = Net force Mass 3. How can you use Newton’s second law to find force? Force = Mass x Acceleration

4. Two ways to increase the acceleration of an object is: a. increase the force acting on it b. decrease the mass of the object

The Third Law of Motion 1. Newton’s third law of motion states: If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.

2. The force exerted by the first object on a second object is the action force. 3. The force exerted by the second object back on the first object is the reaction force.

4. The action and reaction forces in any situation will always be equal and opposite. 5. To determine an object’s momentum, we use the equation Momentum = Mass x Velocity.

6. The law of conservation of momentum states The total momentum of the objects that interact does not change.