mechanics A and B

What is a scalar quantity? 

Give examples

A quantity that has size but no direction

e.g speed, distance, mass, temperature

What is a vector quantity? 

Give examples

A quantity that has size and direction

e.g velocity, displacement, acceleration, force, weight

What are the two ways that vector quantities can be added?

Scale diagram

trigonometry

Describe how you would add two vector quantities using a scale diagram.

Draw the vectors to scale ‘tip to tail’. Measure the resultant vector that would make a triangle

Under what conditions can you use trigonometry to add two vectors.

When the vectors are perpendicular.

What does resolving vectors mean

Splitting vectors into two perpendicular components

How would you resolve a vector into it’s horizontal and vertical components?

Draw a rectangle in which your vector is the diagonal line. Use trigonometry to find the height and base of the rectangle

What is a free body force diagram?

A diagram that shows the forces acting on a body but not the forces it exerts on the rest of the world.

What does it mean if an object is in equilibrium?

The forces on the object cancel each other out so there is no resultant force.

How can you tell if the forces on an object are in equilibrium?

When all the forces on the object are drawn end to end they form a closed shape.

Describe the motion of an object if the resultant force on it is zero?

It will remain stationary or continue at a constant velocity.

Explain the difference between the mass of an object and it’s weight

The mass of an object is how much matter is in it. It doesn’t change when the gravitational field changes.

The weight is the force experienced by the object due to the gravitational field it’s in.

What is a moment

Moment = force x perpendicular distance from the pivot to the line of action of the force.

What does the principle of moments say?

For a body to be in equilibrium the sum of the clockwise moments must equal the sum of the anticlockwise moments

How does a lever work?

Increases the distance between the applied force and the pivot so that a greater load force can be applied.

What is a couple?

A pair of equal and opposite coplanar forces

What is the centre of mass of an object?

The point through which the weight of an object appears to act.

Where is the centre of mass of a uniform, regular solid?

At it’s centre

How would you find the centre of mass of a flat object?

Hang the object from a corner. Use a mass on a string to draw a line directly downwards from the pivot. The C of M is somewhere on this line. Hang the object from a different corner and repeat. The lines cross at the centre of mass.

Define speed

Rate of change of distance, regardless of direction

Give a definition of the displacement of an object

How far an object has travelled from it’s starting point in a given direction.

Define velocity

Rate of change of displacement

Define acceleration

Rate of change of velocity

Under what circumstances can you use the suvat equations?

When the acceleration is constant

In the suvat equations what does ‘s’ stand for?

Displacement

In the suvat equations what does ‘u’ stand for?

Initial velocity

In the suvat equations what does ‘v’ stand for?

Final velocity

In the suvat equations what does ‘a’ stand for?

Acceleration

In the suvat equations what does ‘t’ stand for?

Time

How can you find the velocity of the object from a displacement-time graph?

The gradient of the line

How can you find the acceleration of the object from a velocity- time graph?

The gradient of the line

How can you find the displacement of an object from a velocity- time graph?

The area under the graph