Types of Forces

What are forces? (3)

• A push or pull

• Cause objects to change their motion

• Vector quantity

What unit is force measured in?

Derived unit N (newtons)

N = kg × m/s²

Name 4 the contact forces

• Applied force

• Tension (ropes/ strings)

• Normal (perpendicular to the surface)

• Friction (opposite direction of the object’s motion)

*Applied force and tension occur in the same direction as the object’s motion

Name the action-at-a-distance (non-contact) forces

Gravitational force (always points down towards the Earth)

What are the 4 fundamental forces?

• Gravitational force (attract only)

• Electromagnetic force

• Strong nuclear force

• Weak nuclear force

Equation for the magnitude of the gravitational force

Gravitational force = mass × acceleration of gravity (g)

9 = 9.8 m/s² [down]

What is the net force?

The total force (or resultant) acting on an object

F_net = F₁ + F₂ + … F_n

What is inertia? (2)

• Property of matter that causes objects to resist changes in motion

• Inertia is directly proportional to the mass of the object (objects with more mass have greater inertia, objects with less mass have less inertia)

Newton’s first law of motion (3)

• An object at rest will remain at rest, and an object moving at a constant velocity will remain in motion if the net external force on the object is 0

• uniform motion

• Acceleration = 0 m/s²

What are the 3 implications of Newton’s First law?

• A non-zero net force will change the velocity of an object. The velocity can change in magnitude, direction, or both

• A net force is not required to maintain the velocity of an object

• External forces are required to change the motion. Internal forces do not affect the motion of an object

Newton’s second law of motion (3)

• If the external net force is not 0, the object will accelerate in the direction of the net force. The magnitude of the acceleration is directly proportional to the magnitude of the net force and inversely proportional to the mass of an object

• F_net = ma

• a ∝ F_net (direct proportionality)

• a ∝ 1/ m (inverse proportionality)

Newton’s third law of motion

For every action force, there is a simultaneous reaction that is equal in magnitude but opposite in direction

What are action and reaction forces?

Action and reaction forces are a set of forces that occur when an object exerts a force on another (action force), and the second object exerts a force back (reaction force)