Understanding Force, Motion, and Newton's Laws

What is Force?

Force is a push or pull that can deform an object or change its state of rest or motion.

Types of Forces

• Contact
• Non-contact
• Instantaneous
• Constant

Formula of Force

F = m • a

Difference Between Force and Weight

Weight is a force. Everything on Earth is pulled down towards the ground by gravity. The weight of an object is how hard gravity pulls down on it.

Larger objects get pulled more strongly, so they weigh more than smaller objects. When scientists want to talk about how much stuff is inside something, they talk about mass.

Causes of Force

Forces arise when two or more bodies come into contact. For example, when there is a crash or when you push a door.

Bodies, even if they are not in contact, exert a force on others. For example, the force of attraction of a magnet towards something metallic or the force of gravity itself that the Earth exerts.

What is a Dynamometer?

A dynamometer is an instrument used to measure forces or to calculate the weight of objects.

These devices have a spring with a hook in which we put the object whose weight we want to calculate. The more weight we put, the more the spring is stretched. This is how the weight is measured.

4 Fundamental Interactions

• Strong nuclear force
• Electromagnetic force
• Weak nuclear force
• Gravitational interaction

Newton's Laws

Law of Inertia

If you apply a force to an object of mass (m), you accelerate it in the direction of the force.

Fundamental Principle of Dynamics

Even if the same force is applied to each object, each will reach a different acceleration.

Formula: F = m • a

Law of Action-Reaction

If you apply a force to an object, it will apply a force with the same magnitude but in the opposite direction.

Formula: P = m • g

Hooke's Law

Hooke's law is the one that works with springs to find the weight of the object we are measuring.

The extension or compression of an elastic body is directly proportional to the force applied to it.

F = Force (N)

K = Constant of elasticity (N/m)

X = Stretch (m)

Principal Formula

F = K • X

To Find (K)

K = F / X

To Find (F)

F = m • g

To Find (X)

X = X - X₀ / X = F / K

Direction of Forces

• Downward: P (weight)
• Upward: N/F_n (Normal force)
• Leftward: F_r/F₂ (Friction force)
• Rightward: F/F₁ (Tension force)

Principal Formulas

F = m • a (Normal problems)

F = K • X (Hooke's Law problems)

Last Unit

Formulas for UARM Problems

S = S₀ + V₀ • t + 1/2 a • t² (t squared)

V = V₀ + a • t

a = (V - V₀) / t

t = (V - V₀) / a

Formulas for URM Problems

S = S₀ + v • t

V = (S - S₀) / t

S = v • t

V = s / t

T = (S - S₀) / v

T = s / v

Theory Last Unit

Trajectory: The geometric line that a moving object describes.

Distance traveled: It refers to how far an object moves along a trajectory.

Displacement: It's the distance between two different positions of moving objects (it's measured in a straight line).

Speed: It's the quantity that tells us how quickly bodies change their position.

Position: It's a point on the trajectory determined by a coordinate point.