**length and time**

**1) Describe the use of rules to find a length**

- A rule (ruler) is used to measure length for distances between 1 mm and 1 m.
- For even smaller lengths, use a
**micrometer screw gauge.** - SI unit for length is the meter (m)

**2) Describe the use of measuring cylinders to find a volume**

- To find out volume of regular object, use mathematical formula
- To find out volume of irregular object, put object into measuring cylinder with water. When object added, it displaces water, making water level rise. Measure this rise. This is the volume.

**3) Describe the use of clocks and devices, both analogue and digital, for measuring an interval of time**

- Interval of time is measured using clocks or a stopwatch
- SI unit for time is the second(s)
- To find the amount of time it takes a pendulum to make a spin, time ~25 circles and then divide by the same number as the number of circles.

**motion**

**4) Define Speed and Calculate Average Speed**

- Speed is the distance an object moves in a time frame. It is measured in meters/second (m/s) or kilometers/hour (km/h).
- Speed is a
**scalar**quantity as it only shows magnitude. **Velocity***(v)*is speed in a specified direction, is a**vector**.

\[Average\: speed=\frac{Total\: distance}{Total\: time}\]

**5) Define and Calculate Acceleration**

*(a)*- Acceleration is the rate of change in velocity per unit of time
- It is a vector.
- Positive acceleration means the velocity of a body is increasing
- Deceleration or negative acceleration means the velocity of a body is decreasing
- A curved speed time graph means changing acceleration.

\[Acceleration=\frac{final\: velocity-initial\: velocity}{time\: taken}\]

\[a=\frac{v-u}{t}\]

**6) Interpret a speed-time graph and a distance-time graph**

D-T graph:
gradient = v |
V-T graph:
gradient = aarea under graph = displacement |

**7) Acceleration of Free Fall (**

*g)*- An object in free-fall near to the Earth has a
**constant**acceleration caused by gravity due to the Earth’s uniform gravitational field.

- Objects are slowed down by air resistance.
- When deceleration caused by air resistance = acceleration by gravity, i.e. no net force acting on a body in free fall, the body reached
**terminal velocity**

**mass and weight**

**8) Distinguish between Mass and Weight**

- Mass is a measure of matter in a body and the body’s resistance to motion. SI unit: kg

- Weight
*(W)*is the force of gravity on a body as a result of its mass. SI Unit: Newton (N)

*W = m g*

Weights (and hence masses) may be compared using a balance

**density**

\[density=\frac{mass}{volume}\]

\[\rho=\frac{m}{V} \]

**9) Describe an experiment to determine the Density of a Regularly shaped solid**

- Place the object on the top pan balance and measure its
**mass**. - Use a ruler to measure object dimension, calculate the
**volume**of the cube using mathematical formula. - Find the density of the object using the formula.

**10) Describe an experiment to determine the Density of an Irregularly shaped solid**

- Place the object on the top pan balance and measure its
**mass**. - Fill an eureka can with water until the opening.
- Carefully lower the object into the can, and measure the
**volume**of water displaced. This is the volume of the solid. - Find the density of the object using the formula.

**11) Describe an experiment to determine the Density of a Liquid**

- Place the measuring cylinder on the top pan balance and measure its
**mass**. - Pour a known
**volume**, eg 30 cm3, of the liquid into the measuring cylinder and measure its new mass. - Subtract the mass in step 1 from the mass in step 2. This is the mass of 30 cm3 of water.
- Find the density of the liquid using the formula.

**forces**

**12) Describe Forces**

- A force may produce a change in
**size**and**shape**and**motion**of a body. - Force is measured in Newtons.

__Friction:__- The force between two surfaces which impedes motion and results in heating.
**Air resistance**is a form of friction

__Newton's Law of Motion:__- First law of motion: If no external force is acting on it, an object will, if stationary, remain stationary, and if moving, keep moving at a steady speed in the same straight line
- Second law of motion: F = m x a
- Third law of motion: if object A exerts a force on object B, then object B will exert an equal but opposite force on object A.

**13) State Hooke's Law**

- states that for a spring, 𝐹 = 𝑘𝑥 where F is the force applied to the spring in 𝑁, k is the spring constant in 𝑁𝑚−1 , and x is the extension in 𝑚.
Limit of proportionality: point at which load and extension are no longer proportional.Elastic limit: point at which the spring will not return to its original shape after being stretched. |

**14) Describe the moment of a force**

- A moment is the measure of the turning effect on a body and is defined as:

moment = force × perpendicular distance from the pivot

*m = F x d*Therefore, increasing force or distance from the pivot increases the moment of a force

This explains why levers are force magnifiers ie. turning a bolt is far easier with a wrench because the perpendicular distance from pivot is massively increased, and so is the turning effect.

In equilibrium, clockwise moment = anticlockwise moment, there is no resultant force acting on the body

This can be proven by hanging masses of the same weight on opposite sides of a meter rule on a pivot at equal distances from the pivot showing that the meter rule in stationary.

This explains why levers are force magnifiers ie. turning a bolt is far easier with a wrench because the perpendicular distance from pivot is massively increased, and so is the turning effect.

In equilibrium, clockwise moment = anticlockwise moment, there is no resultant force acting on the body

This can be proven by hanging masses of the same weight on opposite sides of a meter rule on a pivot at equal distances from the pivot showing that the meter rule in stationary.

**15) Centre of Mass**

- Centre of mass: imaginary point in a body where total mass of body seems to be acting.

__Experiment to determine the position of the centre of mass of a plane lamina__

__Describe the effect of the position of the centre of mass on the stability of simple objects__

- If the centre of mass is
**below**the point of suspension of an object, it will be in stable equilibrium (e.g. a hanging plant pot). - If the centre of mass is
**above**the point of suspension of an object, it will be in unstable equilibrium (e.g. a pencil placed on its sharp end). - If the line of action of the object’s weight moves outside the base, there will be a resultant moment and it will topple.

**16) Pressure**

- Pressure is the force per unit area.
- Unit: Pascals (Pa) = N/m2

\[Pressure=\frac{Force}{Area}\]

\[P=\frac{F}{A}\]