P8 - Forces in Balance

What is displacement?

distance in a certain direction

What is a vector?

Physical quantities that have a direction

What is a scalar?

Physical quantities that have no specific direction just size

What is the magnitude?

The size of a quantity

How is a vector quantity represented?

an arrow in the direction of the vector and the length in proportion to the magnitude of the vector.

What is Newton's third law of motion?

This law states that when the two objects interact with each other, they exert equal and opposite forces on each other. The unit of force is newton (n).

What can forces do?

They can change the shape of an object or change its motion or its state of rest.

What is a contact force?

a force that only acts on objects when the two objects interact with each other.

When two objects interact...

They always exert equal and opposite forces on each other.

What is a resultant force?

the overall force acting on an object, taking into account all the different forces acting on it.

What happens if the resultant force is zero?

The object stays at rest or at the same speed

What happens if the resultant force is more than zero?

The speed or direction of the object will change

If two forces act on an object along the same line, the resultant force is:

- Their sum if the forces act in the same direction
- Their difference if the forces act in opposite direction

What type of diagram can be used to show forces acting on an object?

A free-body force diagram

What is the centre of mass on an object?

The centre of mass of an object is the point in which its mass is thought to be concentrated

What is the centre of mass on a ruler?

At the midpoint

Where is the centre of mass on a symmetrical object?

Along the lines of symmetry

What happens at the centre of mass when an object is freely suspended?

When an object is freely suspended, it comes to rest with its centre of mass directly underneath the point of suspension.

What is the parallelogram of forces?

a scale diagram of two force vectors

What is the parallelogram of forces used for?

To find the resultant of two forces that do not act along the same line.

What is the resultant on a parallelogram?

The resultant is the diagonal of the parallelogram that starts at the origin of the two forces.

What is meant by resolving a force?

Means finding perpendicular components that have a resultant force that is equal to the force.

How do you resolve a force in two different directions?

Draw a rectangle with adjacent sides along the two directions so that the diagonal represents the force vector.

What is the resultant force of an object in equilibrium

zero

Why is an object at rest in equilibrium?

because the resultant force is at zero