Forces and Motion Notes

What must a data table include?

Columns with suitable labels including proper units. Enough data including repeat measurements.

What must a distance-time graph include?

Both axes labelled with correct units. Axes scaled so data points cover more than half the graph. Points plotted as (+) with a sharp pencil.

How do you convert one unit of measurement into another?

Identify the conversion factor between the two units, then multiply or divide accordingly (e.g. cm to m: divide by 100; km/h to m/s: divide by 3.6).

How do you calculate speed from raw data?

Speed = total distance travelled ÷ total time taken (s = d/t).

How do you calculate speed from a distance-time graph?

Calculate the slope (gradient) of the line: gradient = rise ÷ run (change in distance ÷ change in time).

How do you draw a distance-time graph from raw data?

Plot time on the x-axis and distance on the y-axis. Label both axes with units. Scale axes so data covers more than half the graph. Plot points as (+) and draw a best-fit line.

What does the slope of a distance-time graph tell you?

Horizontal line = stationary object. Positive slope = moving away from starting point. Negative slope = moving towards starting point. Changing slope = changing speed (acceleration). The value of the slope equals the speed.

What does the slope of a speed-time graph represent?

The slope (gradient) of a speed-time graph represents the acceleration of the object.

How do ticker timers measure speed, and what does dot separation tell you?

A ticker timer makes dots on a tape at regular time intervals. The separation between dots shows speed — dots closer together = slower speed, dots further apart = faster speed.

How do you analyse a ticker tape to calculate acceleration?

1. Calculate speed over equal time intervals (distance between dot groups ÷ time). 2. Plot a speed-time graph using those speeds. 3. Calculate acceleration at various times using the gradient of the speed-time graph (a = change in speed ÷ time).

What are the two types of forces? Give examples.

Contact forces: forces that require physical contact (e.g. friction, tension, normal force). Non-contact forces: forces that act at a distance (e.g. gravity, magnetism, electrostatic force).

State Newton's Third Law of Motion.

For every force, there is an equal and opposite force. (If object A exerts a force on object B, object B exerts an equal force in the opposite direction on object A.)

What apparatus is used to measure force?

A newton meter (also called a spring balance or force meter), measured in Newtons (N).

What is the difference between mass and weight?

Mass: the amount of matter in an object — remains CONSTANT regardless of location (measured in kg). Weight: the force of gravity acting on an object — depends on gravitational field strength and changes with location (measured in Newtons, N).

State Newton's First Law of Motion.

A stationary object will remain stationary unless a force acts on it. An object moving at constant speed will continue at that speed unless a force acts on it. (Objects resist changes to their motion — this is inertia.)

What is the link between force, mass and acceleration?

Force = mass × acceleration (F = ma). Greater force on the same mass = greater acceleration. Greater mass with the same force = lower acceleration.

State Newton's Second Law of Motion.

The force on an object equals its mass multiplied by its acceleration: F = ma. A force of 1 Newton accelerates 1 kg at 1 m/s². For a given force, greater mass = lower acceleration. For a given mass, greater force = greater acceleration. Acceleration = Force ÷ mass (a = F/m).

What is deceleration and what direction is the force?

Deceleration is the slowing down of an object (negative acceleration). The force causing deceleration acts in the OPPOSITE direction to the object's motion.

What does "energy" mean in science?

Energy is the capacity to do work — it is what allows forces to move objects and cause changes. It is measured in joules (J) or kilojoules (kJ).

State the Law of Conservation of Energy.

Energy comes in different forms. Energy cannot be created or destroyed. Energy can be changed from one form into another. Energy is measured in joules (J) or kilojoules (kJ).

What is the link between energy change and work?

Any energy change in an object is associated with work being done on or by that object.

What is work?

Work is the amount of energy transferred when an object is moved by a force.

What is the formula for work done?

Work done = Force × distance moved in the direction of the force. W = F × d. Units: joules (J), where force is in Newtons (N) and distance is in metres (m).

What is power?

Power is the rate at which work is done — how quickly energy is transferred.

What is the formula for power?

Power = energy change ÷ time taken for the energy change. P = E/t. Power is measured in Watts (W), which equals Joules per second (J/s).

What are the units of power?

Watts (W), which is equivalent to Joules per second (J/s).

How do you measure your own power output?

Measure the work done (force × distance, e.g. your weight × height of stairs climbed) and divide by the time taken: P = W/t.