Understanding joules and newtons is important for figuring out how energy, work, and force work in our world. Let’s look at some everyday situations to see how these ideas fit into Year 8 Physics.

Real-World Examples of Joules (J):

1. Lifting an Object:

   • When you lift a backpack from the ground to your shoulder, you have to push against gravity.
   • This takes energy, which we measure in joules.
   • For example, if your backpack weighs 10 kg, we calculate the force acting on it like this:
     • Weight = mass × gravity = 10 kg × 9.8 m/s² = 98 N
   • If you lift it up 1.5 m, we find out how much work you did using:
     • Work = force × distance = 98 N × 1.5 m = 147 J
   • So, lifting that backpack requires 147 joules of energy.

2. Running:

   • When you run, your body works against friction and air pushing back.
   • The energy you use while running can also be measured in joules.
   • For example, if someone weighing 70 kg runs up a 5 m hill, we can find out the work done against gravity like this:
     • Work = mass × gravity × height = 70 kg × 9.8 m/s² × 5 m = 3430 J
   • This means you need 3430 joules of energy to run up the hill.

3. Heating Water:

   • Heating water requires energy measured in joules too.
   • For instance, if you want to boil 1 liter of water, starting from room temperature (about 20 °C) to 100 °C, we can calculate the energy needed.
   • The specific heat of water is around 4.18 J/g°C. So, to heat 1000 grams of water:
     • Energy = mass × specific heat × change in temperature
     • Energy = 1000 g × 4.18 J/g°C × (100 - 20)°C = 33440 J
   • This tells us that 33440 joules are needed to bring the water to a boil.

Real-World Examples of Newtons (N):

1. Everyday Forces:

   • When you push a shopping cart, you use a force measured in newtons.
   • If you push with a force of 50 N, this helps us understand how we move objects.
   • If there is also friction pushing back with the same force, we can look at total forces using Newton's laws.

2. Gravity and Weight:

   • The weight of an object is a simple example of newtons in action.
   • For example, if a child weighs 30 kg, the gravity acting on them can be calculated like this:
     • Force = mass × gravity = 30 kg × 9.8 m/s² = 294 N
   • So, the child weighs 294 newtons.

3. Throwing a Ball:

   • When you throw a ball, you apply a force to it.
   • If you use a force of 10 N to throw the ball, this force helps it move forward.
   • Understanding how this force works is important in sports and physics.

How Joules and Newtons Relate in Work:

The link between joules and newtons becomes clear when we look at how work is done:

1. Work Done (W):

   • Work happens when a force (in newtons) moves something over a distance (in meters).
   • The formula for work is:
     • Work = force × distance
   • Here, work is in joules, force is in newtons, and distance is in meters. This shows how force and energy are connected.

2. Example Calculation:

   • If you push something with a force of 20 N over a distance of 3 m:
     • Work = force × distance = 20 N × 3 m = 60 J
   • So, you’ve done 60 joules of work.

By looking at these examples, we can see how these ideas in physics apply to our everyday lives. Knowing how joules and newtons are part of our day-to-day experiences helps us understand why they are important in the study of energy and force.