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Physics - Forces and motion (push, pull, and friction)

Grade 4Cambridge (IGCSE)

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 on an object. Forces can make objects start moving, stop moving, change speed, or change direction.

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Forces are measured in Newtons, which is represented by the symbol NN.

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We use a device called a force meter (or Newton meter) to measure the size of a force.

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Friction is a force that occurs when two surfaces rub against each other. It always acts in the opposite direction to the motion.

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Smooth surfaces (like ice or glass) create less friction, while rough surfaces (like sandpaper or carpet) create more friction.

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Air resistance and water resistance are types of friction that slow down objects moving through air or water.

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Forces can also change the shape of an object (stretching, squashing, or twisting).

📐Formulae

Net Force=Forcepush−ForcefrictionNet\ Force = Force_{push} - Force_{friction}

Weight (N)=mass (kg)×10 N/kgWeight\ (N) = mass\ (kg) \times 10\ N/kg

Total Force=F1+F2 (if acting in the same direction)Total\ Force = F_1 + F_2 \text{ (if acting in the same direction)}

💡Examples

Problem 1:

A toy car is pushed across a floor with a force of 10 N10\ N. The friction between the wheels and the floor is 3 N3\ N. What is the total force acting on the car?

Solution:

10 N−3 N=7 N10\ N - 3\ N = 7\ N

Explanation:

Since friction acts in the opposite direction to the push, we subtract the friction force from the pushing force to find the net force of 7 N7\ N.

Problem 2:

An object has a mass of 2 kg2\ kg. What is its weight on Earth where gravity is approximately 10 N/kg10\ N/kg?

Solution:

2 kg×10 N/kg=20 N2\ kg \times 10\ N/kg = 20\ N

Explanation:

Weight is the force of gravity pulling on an object. To find it, we multiply the mass by the gravitational pull (10 N/kg10\ N/kg).

Problem 3:

If two students are pulling a rope in a game of tug-of-war, and Student A pulls with 50 N50\ N to the left while Student B pulls with 50 N50\ N to the right, what is the resulting movement?

Solution:

50 N−50 N=0 N50\ N - 50\ N = 0\ N

Explanation:

The forces are balanced because they are equal in size but opposite in direction. Therefore, the net force is 0 N0\ N and the rope does not move.