Physics - Mechanics 1 (Section 4)

Give examles of Scalar Quantities

Time, Distance, temperature, mass, speed, length, energy

What is the difference between scalar and vector quantities?

Scalars have a magnitude only, whereas vectors have a magnitude and direction.

Give examples of vectors

Weight, force, momentum, displacement, velocity, acceleration

What is important to remember about inclined plane problems?

W > W1 W>W2, therefore in right angled triangles with W1/W2 and W, W must be the hypotenuse

What are free body diagrams

Diagrams showing all forces exerted on a single object

What is Newton’s first law

If there are not resultant forces acting on an object then it will either remian at rest, or travelling at a constant speed/velocity in a straight line.

How to calculate resultant forces?

Draw forces tip to tail, the resultant force is from the first arrow to the end of the last arrow (closed vector triangles are formed in object is in equilibrium).

What is a moment?

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

What is the principle of moments?

If a system is in equilibrium then the sum of the clockwise moments = the sum of the anti-clockwise moments (CM=ACM)

What is the centre of mass?

The point in which you can consider all the weight (of the object) acts through, no matter the orientation.

How to find the mass of an object experimentally?

• Cut a piece of card into any shape'

• Hang the card from a point (with a string and plumbob attached)

• Mark a straight line along the string (repeat at least twice)

• The point of intersection is the centre of mass

What concept do engineers use to improve stability.

The centre of mass with the concept of moments:

• A low centre of mass increases stability as tilting creates a moment to tip the object back onto its base

• A low and wide base increases stability.

When does an object topple?

The object topples when the line of action of its weight (acting through the centre of mass) falls outside the the base of support

What is the principle of moments?

If a system is in equilibrium then the

What does each letter in SUVAT stand for

• s = displacement

• u = initial velocity

• v = final velocity

• a = acceleration

• t = time

What needs to be true when using SUVAT equations in questions?

For it to be uniform acceleration.

State the four SUVAT equations needed.

• v² = u² + 2as

• v = u + at

• s = ut + 0.5at²

• s = 0.5(u+v)t

What does the gradient of a displacement-time graph represent, including what is means if it is a horizontal line, straight line and curved line.

• Gradient = Velocity

• Horizontal line = Stationary

• Straight line = Constant velocity

• Curved line = acceleration

How do you find the velocity at a certain time for a curved displacement time graph?

• Draw a tangent at that point

• Find the gradient of the tangent

What do the gradient, the area under the line, a horizontal line, a straight line and a curve of a velocity time graph represent?

• Gradient = acceleration

• Area under the line = change in displacement

• Horizontal line = Constant velocity

• Straight line = Constant acceleration

• Curved line = Change of acceleration

Explain the two methods to find the area under a graph?

• Divide graph into triangles and rectangles (/into a trapezium)

• Count the number of whole squares under the line and count each partial square as ½ a square, then multiply the number of squares by the area of one square.

What does the area under the line, a horizontal line and a line under the x-axis represent in an acceleration-time graph?

• Area under the line = Change in velocity

• Horizontal line = Constant acceleration

• Line under x-axis = Negative acceleration/deceleration