# This Study Stack is to help you study for Force & Motion

Define "force". Force is described by its strength and by the direction in which it acts. It is a "push" or "pull"
What is the SI unit of measure for force? The SI unit of measure for force is a "newton" (N).
Define "net force". Net force is the combination of all forces acting on an object.
How do you find net force? Same direction – add the forces
Opposite direction – combine by subtracting
Define "unbalanced force". Whenever there is a net force acting on an object the forces are unbalanced and there is motion.
Define "balanced force". Balanced forces are equal forces acting on one object in opposite directions. There is no motion.
Define "friction". Friction is the force that two surfaces exert on each other when they rub agains each other.
What causes friction? The strength of the force of friction depends on two factors: how hard the surfaces push together and types of surfaces involved.
Name the 4 types of friction. static, sliding, rolling, and fluid
Define "static friction". The friction that acts on objects that are not moving is static friction.
Define "sliding friction". Sliding friction occurs when two solid surfaces slide over each other.
Define "rolling friction". When an object rolls across a surface, rolling friction occurs.
Define "fluid friction". Fluid friction occurs when a solid object moves through a fluid.
Define "gravity". Gravity is a force that pulls objects toward each other.
Explain universal gravitation. The law of universal gravitation states that the force of gravity acts between all objects in the universe.
What 2 factors affect gravity? Mass and distance affect gravity.
Define "weight". Weight is the force of gravity on an object.
Explain free fall. Free fall is when the only force acting on an object is gravity.
Explain air resistance. Air resistance is the upward force exerted on falling objects. Air resistance is not the same for all objects. Objects with greater surface area experience more air resistance.
Define "projectile". An object that is thrown is called a projectile.
How does gravity affect objects moving horizontally? Gravity pulls the object toward the center of the Earth in the same way it pulls a dropped object.
What is Newton's 1st Law of Motion? An object at rest remains at rest and an object in motion remains in motion unless acted upon by an outside force.
Define "inertia". Inertia is the tendency of an object to resist a change in motion.
How is mass related to inertia? The greater the mass of an object, the greater its inertia and the greater force needed to change its motion.
What is Newton's 2nd Law of Motion? Acceleration depends on the object's mass and on the net force acting on the object.
What is the equation for Newton's 2nd Law of motion? Acceleration = Net Force
Mass
What are two ways to increase the acceleration of an object? To increase acceleration, you can decrease mass or increase force.
What is Newton's 3rd Law of Motion? For every action there is an opposite and equal reaction.
Why don't action/reaction forces cancel each other? Action/Reaction forces do not cancel each other because they act on different objects.
Define "momentum". Momentum is a characteristic of a moving object tht is related to the mass and the velocity of the object.
What is the formula for momentum? Momentum = Mass X Velocity
Explain conservation of momentum. The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects.