This section tests your knowledge on physical properties of motion and sound.
Let’s talk about some concepts bound to pop up on the test.
Laws of Motion
Sir Isaac Newton developed three laws of motion to describe how bodies interact. These may seem obvious today, but his laws set the foundation for modern physics. Remember that a force is a push or pull on an object, and external forces are any outside forces that act on something. We measure the force in Newtons (N). Friction causes objects to slow down, and inertia is the tendency of an object to remain at rest or in motion. Equilibrium occurs when the forces on the system are balanced.
Newton’s First Law: This law is also known as the law of inertia. This law states that an object at rest will stay at rest until a force acts on it. Similarly, an object in motion stays in motion unless an external force acts on it. This means that things can’t stop or start randomly by themselves. It takes a force to change it. If you slide a hockey puck across the ice, it will eventually stop because of the friction of the ice against the puck. The puck doesn’t just randomly start sliding. You had to initiate the sliding.
Newton’s Second Law: This law explains that when a constant force acts on a body, it causes the body to accelerate and change its velocity at a constant rate. The force acting on an object is equal to the mass of the object times its acceleration. This is often written as the formula: F= m *a, where F= force, m = mass, and a = acceleration. The more mass an object has, the more force you need to move it. For example, it’s easier to push an empty shopping cart than a full one. The full cart has more mass and requires more force to move it.
Newton’s Third Law: For every action (force), there is an equal and opposite reaction. Forces always occur in pairs. When a body pushes against another, the second body pushes back with equal amount of force. When you’re on a skateboard and you push backward, the same amount of force drives the skateboard forward. When you throw a ball to the ground, it bounces back with equal amount of force.
A wave is any transfer of energy from one point to another without a transfer of material. A wave is a disturbance that travels through a medium, transporting energy without transporting the matter. A wave can be an ocean wave, but we can also think of sound waves, where vibrations of air molecules carry energy from one place to another. When drawing a wave on a graph, the highest point of the wave is called the crest, and the lowest point is called the trough.
We can explain waves based on their characteristics. Waves can be transverse or longitudinal.
Transverse waves occur when the particles move in a direction perpendicular to the direction the wave moves. When you picture the vibration of strings, ripples on water surface, an audience doing the “wave,” or light waves, these are all transverse waves.
Longitudinal waves occur when the particles move parallel to the direction of the wave. An ocean wave, ripples from a stone across a pond, and sound waves are all longitudinal.
There are several words we use to describe the qualities of a wave:
Frequency: The number of times per second that the wave cycles. Frequency is measured in Hertz, or the letter (f).
- Amplitude: This is measured by the difference in the height of the wave (crest) and the wave at resting position. This measures the displacement of the wave from rest, and measures the overall intensity. When thinking about sound waves, the amplitude measures the loudness of the sound.
- Wavelength: The distance between two wave cycles. This is measured by the distance between two crests or two troughs (two high points or two low points). Wavelength is represented by the Greek letter lambda (λ).
- Speed: Speed measures how fast the wave is moving. This is the horizontal speed of a point on the wave, measured in meters per second (m/s).
- Energy: Waves transfer energy without matter.
And that’s some basic info about the Physical Science content category.