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Forces and Motion - Measuring the strength of forces

Grade 3IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A force is a push or a pull that acts upon an object as a result of its interaction with another object.

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The strength of a force is measured in units called Newtons (NN), named after Sir Isaac Newton.

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A force meter, also known as a spring balance or Newton meter, is the instrument used to measure the size of a force.

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Inside a force meter is a spring. When a force is applied (like a pull), the spring stretches. The larger the force, the more the spring stretches, moving a pointer along a scale.

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Weight is a type of force caused by gravity pulling an object toward Earth. Since weight is a force, it is measured in Newtons (NN), not kilograms (kgkg).

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Friction is a force that acts in the opposite direction to motion, and it can also be measured using a Newton meter by pulling an object across a surface.

📐Formulae

Weight (N)=Mass (kg)×Gravity (N/kg)\text{Weight (N)} = \text{Mass (kg)} \times \text{Gravity (N/kg)}

W=m×gW = m \times g

Total Force=F1+F2\text{Total Force} = F_1 + F_2

💡Examples

Problem 1:

A student hangs a toy robot on a Newton meter. The pointer moves down and stops at the mark 44. What is the weight of the toy robot?

Solution:

The weight is 4 N4\text{ N}.

Explanation:

The Newton meter measures the force of gravity pulling on the robot. Since the pointer is at 44, the force (weight) is 44 Newtons.

Problem 2:

If a small stone has a mass of 0.1 kg0.1\text{ kg} and the Earth's gravity is approximately 10 N/kg10\text{ N/kg}, use the formula W=m×gW = m \times g to find its weight.

Solution:

W=0.1 kg×10 N/kg=1 NW = 0.1\text{ kg} \times 10\text{ N/kg} = 1\text{ N}

Explanation:

To find the weight, we multiply the mass by the gravitational strength. 0.10.1 multiplied by 1010 equals 11 Newton.

Problem 3:

You are pulling a wooden block across a table. The force meter reads 2 N2\text{ N} to keep it moving at a steady speed. If you add a heavy weight on top of the block, will the force meter reading increase or decrease?

Solution:

The reading will increase (>2 N> 2\text{ N}).

Explanation:

Adding weight increases the friction between the block and the table. A larger force is needed to overcome this friction, which causes the spring in the force meter to stretch further.