Physics Unit 3: Forces

What is weight and its formula?

Weight is the effect of a gravitational force acting on an object’s mass in a gravitational field. W = mg

Measuring Tool: Spring balance.

What is mass?

Mass is the measure of the quantity of matter in an object at rest relative to the observer.

→ Mass is the property of an object that resists changes in motion.

MEASURING TOOL: Electronic balance.

What is the formula for force?

F = ma

F = Δ p / Δ t

What is gravitational field strength and its formula?

Gravitational field strength is the force per unit mass acting on an object in a gravitational field. (*Gravitational field strength and acceleration of free fall are equivalent quantities.)

g = W/m

What is momentum and what is the formula for momentum?

An object with mass that is in motion has momentum. Momentum is vector, so it can be POSITIVE or NEGATIVE. p = mv

State the principle of conservation of momentum.

The total momentum of an object BEFORE it collides with another is EQUAL to the total momentum AFTER the collision.

What is the formula for impulse?

Δ p = Δ(mv) OR mv - mu

Δ p = FΔt

What is the forces involved in circular motion and how do they work?

In circular motion, the velocity of the object is constantly changing, as the direction changes as the object moves in a circle. This means there is acceleration in circular motion, meaning the object has the forces of weight/gravitational force, tension and friction acting on it to keep it moving. These unbalanced forces are named centripetal forces, which are the forces keeping the body moving in a circle.

The centripetal forces are PERPENDICULAR to the velocity of the object.

The velocity of the object moving in a circle is a tangent to the circular orbit motion of the object.

The force that keeps an object attached to a STRING when it is moving in a circle is the TENSION. If an object tethered to a string is in circular motion, and it is suddenly cut from the string and released, it will move in the direction in which it was moving.

Even if a full circular path isn’t completed, it’s still circular motion as it is PART of a circle.

What are the factors affecting circular motion?

1. Mass: Larger = LARGER force

2. Radius of the circle in which the body is moving in: Smaller = LARGER force

3. Speed: Larger = LARGER force

→ Greater speed, greater force. Smaller radius, greater force. Greater mass, greater force.

Explain concepts of free fall, terminal velocity and why objects will reach the ground in the same time if we drop them from the same height.

When we drop objects (no matter the mass) from the SAME height, they will reach the ground at the same time as the acceleration is equal.

→ Surface area AFFECTS how QUICKLY an object reaches the ground due to AIR RESISTANCE. Increased surface area = increased air resistance.

→ Free fall: when an object accelerated due to gravity in the ABSENCE of any other FORCES such as air resistance. In free fall, the only force acting on the object is weight.

→ When an object falls, two forces act on it: weight and air resistance. When these two forces eventually equate one another, we will reach TERMINAL VELOCITY, which is the MAXIMUM CONSTANT SPEED an object can reach when MOVING THROUGH A FLUID.

Factors affecting air resistance are:

1. Surface area: When it increases, air resistance increases.

2. Density of air: When it increases, air resistance increases.

3. Speed of objects: When it increases, air resistance increases.