Lesson 1 - Forces

Term 3 - Physics
Forces and Motion

This term...

Forces and motion are fundamental concepts in physics that describe how objects move and interact with each other. Here's a brief description suitable for Year 7 students:

Forces

Forces are pushes or pulls that can make objects move, stop, or change direction. They can be contact forces (like when you push a door) or non-contact forces (like gravity, which pulls objects towards the Earth). Examples of forces include:

• Gravity: The force that pulls objects towards the center of the Earth.

• Friction: The force that resists the movement of one surface against another.

• Push and Pull: When you push a shopping cart or pull a drawer open.

Motion

Motion is the change in position of an object over time. It can be described in terms of speed, direction, and how far an object moves. When we talk about motion, we often consider:

• Speed: How fast an object is moving.

• Velocity: Speed in a given direction.

• Acceleration: The rate at which an object's velocity changes.

Forces and Motion

For example, when you ride a bike, you can feel different forces acting on you: your legs apply a force to pedal, friction between the tires and the ground helps you move forward, and gravity pulls you down. The combination of these forces causes the motion of the bike.

Understanding forces and motion helps us explain how things move and interact in our everyday lives, from playing sports to driving cars.

What do forces do?

We can't see forces, but we can see their effects on objects. Without forces, nothing would begin moving, stop moving, change direction or change speed.

There are six effects that forces can have on an object. Forces can:

1. Change the shape of an object

2. Change the direction of an object

3. Cause something to start moving

4. Cause something to stop moving

5. Speed up an already moving object

6. Slow down an already moving object

Multiple Choice

An empty soft drink can is crushed. The effect of the force is to:

• Speed up the object

• Stop the object moving

• Start the object moving

• Change the shape of the object

Multiple Choice

A golf ball is not moving A force is applied as the golfer hits it. The effect of the force is to:

• Speed up the object

• Stop the object moving

• Start the object moving

• Change the shape of the object

Multiple Choice

A piece of toast is dropped. A force is applied when it hits the floor. The effect of the force is to:

• Speed up the object

• Stop the object moving

• Start the object moving

• Change the shape of the object

Multiple Choice

A force is applied when a rollercoaster starts to move down a slope. The effect of the force is to:

• Speed up the object

• Stop the object moving

• Start the object moving

• Change the shape of the object

In your workbooks..

Provide an example for each of the following.
Effect of force Example
Start an object moving
Stop an object moving
Speed an object up
Slow an object down
Change direction
Change shape

Forces Arrows

In a diagram, we can represent the forces that act on an object using arrows.

Each arrow shows:

• the strength of the force: the longer the arrow, the stronger the force

• the direction in which the force is acting

The arrows can be used to predict the motion of an object based on the forces that are applied to it.

For example, the image on the right shows two dogs playing with a toy. The larger dog is pulling on the toy with a stronger force. This is shown by the longer arrow pointing to the left. The toy will move towards the left.

More Types of Forces

Gravity is a natural force that pulls objects towards each other. The most familiar example is the gravitational pull of the Earth, which attracts objects towards its center, giving them weight. This force is what makes things fall when you drop them and keeps us grounded on the Earth's surface. Gravity also governs the motion of planets, stars, and galaxies in the universe.

More Types of Forces

Magnetism is a force that can attract or repel objects that have a magnetic material, such as iron, nickel, or cobalt. Magnets have two poles: north and south. Opposite poles attract each other, while the same poles repel. This force is used in various applications, such as in compasses to show direction, in electric motors to create motion, and in everyday items like fridge magnets.

More Types of Forces

Tension is a force that is transmitted through a string, rope, cable, or any other flexible connector when it is pulled tight by forces acting from opposite ends. For example, when you pull on a rope in a tug-of-war, the rope transmits the force from your hands to the other end. Tension keeps the rope tight and can be seen in structures like bridges and elevators, where cables support weight and allow for movement.

More Types of Forces

Applied forces are forces that are applied to an object by a person or another object. This can include any push or pull exerted on an object to make it move or change direction. For instance, when you push a book across a table, your hand is applying a force to the book. Applied forces can cause objects to start moving, stop moving, or change their speed or direction of motion.

Contact and Non-contact forces

Forces can be classified into two groups. If objects need to be touching for a force to arise, it's known as a contact force. For example, friction occurs when you rub your hands together and air resistance slows down a moving object that's in contact with air.

Forces that don't need contact to have an effect are known as non-contact forces. For example, magnets can push or pull on objects without touching them.